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In this undated photo provided by Prifysgol Aberystwyth University researchers David Whitworth, left, and Sara Mela, pose for photo in the lab at Prifysgol Aberystwyth University in Aberystwyth, Wales. According to results published online Monday, July 28, 2014, in the American Journal of Infection Control the researchers found that the knocking of knuckles, fist bump, spreads only one-twentieth the amount of bacteria that a handshake does. (AP Photo/Prifysgol Aberystwyth University) ( Fist Bumps Germs )

President Barack Obama fist-bumps AbilityOne custodian, Lawrence Lipscomb, in a federal office building following the opening session of the White House Forum on Jobs and Economic Growth. Credit: Official White House Photo by Pete Souza. (PRNewsFoto/AbilityOne, Pete Souza) ( ABILITYONE PRESIDENT BARACK OBAMA AND LAWRENCE LIPSCOMB )

This undated inverted image provided by Prifysgol Aberystwyth University shows powder transferred following handshake, to illustrate possible transfer of bacteria at Prifysgol Aberystwyth University in Aberystwyth, Wales. According to results published online Monday, July 28, 2014, in the American Journal of Infection Control researchers found that the knocking of knuckles, fist bump, spreads only one-twentieth the amount of bacteria that a handshake does. (AP Photo/Prifysgol Aberystwyth University) ( Fist Bumps Germs )

The Dodgers' Clayton Kershaw fist bumps Tremor before pitching for the Quakes at LoanMart Field in Rancho Cucamonga, CA, Friday, April 25, 2014. (Photo by Jennifer Cappuccio Maher/Inland Valley Daily Bulletin) ( 0426_NWS_IDB_L-KERSHAW-01-JCM )

Democratic presidential candidate Sen. Barack Obama (D-IL) (R) and his wife Michelle Obama bump fists at an election night rally at the Xcel Energy Center June 3, 2008 in St. Paul, Minnesota. Obama clinched the Democratic presidential nomination following today's primaries in South Dakota and Montana, although his rival Sen. Hillary Clinton (D-NY) has not yet conceded the race. (Photo by Scott Olson/Getty Images) ( 81348798SO022_OBAMA_HOLDS_F )

Blake Shelton, center, performs at the 48th Annual Academy of Country Music Awards at the MGM Grand Garden Arena in Las Vegas on Sunday, April 7, 2013. (Photo by Chris Pizzello/Invision/AP) ( 48th Annual Academy of Country Music Awards - Show )

Chadwick's Greg Stone, left, and Ethan Leff, right, fist bump on the second hole against Peninsula in a round of golf Tuesday at the Palos Verdes Golf Club. 20120410 (Photo by Steve McCrank /Daily Breeze)

Los Angeles Mayor Antonio Villaraigosa (L) gives a "fist bump" to presumptive Democratic presidential nominee Sen. Barack Obama (D-IL) during the national convention of the League of United Latin American Citizens (LULAC) at the Washington Hilton July 8, 2008 in Washington, DC. Obama has been recently criticized for moving to the political center after calling for a slowing of withdrawal of troops from Iraq, supporting a proposed wiretap law and government funding of faith-based programs. (Photo by Chip Somodevilla/Getty Images) ( 55272087 )

Los Angeles Angels' Mike Trout (27) fist bumps with teammate Albert Pujols (5) after his solo home run in the first inning of a baseball game against the Kansas City Royals at Kauffman Stadium in Kansas City, Mo., Thursday, May 23, 2013. (AP Photo/Orlin Wagner) ( Angels Royals Baseball )

Holding American flags, Boston Marathon bombing survivor Jeff Bauman, left, bumps fists with Carlos Arredondo near the finish line of the the 118th Boston Marathon, Monday, April 21, 2014, in Boston. (AP Photo/Elise Amendola) ( Boston Marathon )

Long Beach City College's Jaime Valle (18), center, gets a fist bumps after singling against Cerritos College during their game in Long Beach, Calif. on March 6, 2012.. (Jeff Gritchen/Long Beach Press-Telegram) ( Long Beach City College Baseball vs. Cerritos College )

Point guard Odyssey Sims gets a fist bump from President Barack Obama at a ceremony honoring the 2012 NCAA Women's basketball champions Baylor University Bears in the East Room at the White House in Washington, Wednesday, July 18, 2012. (AP Photo/Charles Dharapak) ( Obama NCAA Baylor Basketball )

Los Angeles Dodgers third base coach Larry Bowa bumps fists with Los Angeles Dodgers' Andre Ethier #16 after Ethier's triple in the 5th inning during their game against the St. Louis Cardinals at Dodger StadiumTuesday, August 18, 2009. (Hans Gutknecht/L.A. Daily News) ( Los Angeles Dodgers vs St. Louis Cardinals )

Kristian Ipsen, left, and Troy Dumais bumps fists before a dive in the men's in the 3-meter synchro springboard final at the U.S. Olympic diving trials on Friday, June 22, 2012, in Federal Way, Wash. The two won the event. (AP Photo/Elaine Thompson) ( US Diving Trials )

Westchester's Nick Goff (24) bumps fists with Matthew Kanfer as they begin the scoring in the first inning against Torrance in a Babe Ruth final at Kendall Park in Torrance Thursday. Westchester won the first game 6-5. (Photo by Steve McCrank / Staff Photographer)

U.S. President Barack Obama "fist bumps" an audience member after a town hall style event at the University of Malaya with participants in the Young Southeast Asian Leaders Initiative in Kuala Lumpur, Malaysia, Sunday, April 27, 2014. With the first visit to Malaysia by a U.S. president in nearly half a century, Obama holds economic and security talks with Malaysian Prime Minister Najib Razak, who leads a southeast Asian nation with an important role in Obama's efforts to forge deeper ties with the region. (AP Photo/Charles Dharapak) ( Malaysia US Obama )

Clayton Kershaw #22 and Zach Greinke #21 of the Los Angeles Dodgers fist bump in the sixth inning against the Arizona Diamondbacks at Chase Field on April 12, 2014 in Phoenix, Arizona. (Photo by Jason Wise/Getty Images) ( 477580019AM00022_LOS_ANGELE )

CSU Chancellor Timothy P. White gives nursing student Victoria Bowman, left, a fist bump after the two tag-teamed to revive a training dummy with CPR. White spent the day touring Cal State Long Beach on Monday, October 14, 2013. (Photo by Scott Varley, Daily Breeze) ( -L-CHANCELLOR )

Palos Verdes catcher Joe Caparis (40) and pitcher Erik Gutierrez (6)fist-bump after knocking down South batters in an Anaheim Lions Tournament baseball game Tuesday, April 01, 2014, in Palos Verdes Estates, CA. Palos Verdes won 8-0. (Photo by Steve McCrank / Daily Breeze)

Republican vice presidential candidate, Rep. Paul Ryan, R-Wis., fist bumps supporters during a campaign rally in Milwaukee, Wis., Monday, Nov. 5, 2012. (AP Photo/Mary Altaffer) ( Romney 2012 )

Oklahoma head coach Sherri Coale fist bumps with forward Felisha Gibbs, right, during a team practice for the Big 12 women's NCAA college basketball tournament in Oklahoma City, Friday, March 7, 2014. Oklahoma faces Texas on Saturday. (AP Photo/Sue Ogrocki) ( B12 Oklahoma Basketball )

Denver Broncos fans Lonnie Moreno, left, of Denver, and Steve Aviles, of Union City, N.J., bump fists as they tour the Super Bowl Boulevard in Times Square, Friday, Jan. 31, 2014, in New York. The Broncos play the Seattle Seahawks on Sunday in NFL football's Super Bowl in East Rutherford, N.J. (AP Photo/ Evan Vucci) ( Super Bowl Football )

3/29/10 - St. Joseph's Yasmin Cruz gets a fist bump from her coach at first base during a game against St. Paul on Monday afternoon. The Jesters won 7-1. (Photo by Brittany Murray / Press Telegram)

Philadelphia eagles quarterback Michael Vick give seven-year-old Justin Perales a fist bump during a tour of the Eagles training facility in Philadelphia. Four years after his release from prison, Vick is one of the NFL's most active players involving charities. Though he’s no longer the starting quarterback for the Eagles, he’s unquestionably the team leader. (AP Photo/ Joseph Kaczmarek) ( Eagles Vick The Leader Football )

FILE - In this Sept. 23, 2013, file photo, Denver Broncos quarterback Peyton Manning (18) bumps fists with strong safety Mike Adams (20) after beating the Oakland Raiders 37-21 in an NFL football game in Denver. At 37, with four surgical scars on his neck to match the four MVP awards in his trophy case, Denver's quarterback is off to the best start of his storied career. (AP Photo/Jack Dempsey, File) ( Broncos Meticulous Manning Football )

Billionaire Dallas Mavericks NBA basketball team owner Mark Cuban gets a fist bump as he walks with his legal team to the federal courthouse after a break in his insider trading trial in Dallas, Wednesday, Oct. 16, 2013. Jurors say billionaire Mark Cuban did not commit insider-trading when he sold his shares in an Internet company in 2004 after learning of a development that would dilute the value of his investment. The jury in federal court found that the SEC failed to prove several key elements of its case, including that Cuban traded on nonpublic information. (AP Photo/LM Otero) ( Cuban Insider Trading )

President Barack Obama acknowledges the crowd as he exchanges fist bumps with the audience after speaking at Hyde Park Academy, Thursday, Feb. 14, 2013, in Chicago. (AP Photo/M. Spencer Green) ( Obama )

Celebrity judge Howie Mandel arrives at the "America's Got Talent" auditions on Tuesday April 9, 2013 in New York. (Photo by Evan Agostini/Invision/AP) ( America's Got Talent Auditions )

Dale Earnhardt Jr., fist-bumps fans during driver introductions for the NASCAR Sprint Cup auto race at Richmond International Raceway in Richmond, Va., Saturday, April 26, 2014. (AP Photo/Steve Helber) ( NASCAR Richmond Auto Racing )

Felicia Zhang and Nathan Bartholomay of the United States bump fists as they wait in the results area after competing in the pairs short program figure skating competition at the Iceberg Skating Palace during the 2014 Winter Olympics, Tuesday, Feb. 11, 2014, in Sochi, Russia. (AP Photo/Darron Cummings) ( Sochi Olympics Figure Skating )

Vice Chairwoman of the Democratic National Committee Donna Brazile, left fist bumps Director Spike Lee before the skills competition at the NBA All Star basketball game, Saturday, Feb. 15, 2014, in New Orleans. (AP Photo/Bill Haber) ( NBA All Star Saturday Basketball )

In this May 22, 2009 file photo, President Barack Obama fist bumps Chauncy Lorrell Gray, from Chicago, as he approaches the stage to receive his diploma at the United States Naval Academy graduation ceremony in Annapolis, Md. The familiar knocking of knuckles spreads only one-twentieth the amount of bacteria that a handshake does, researchers report. That's better than a high-five, which still passes along less than half the amount as a handshake. (AP Photo/Charles Dharapak, File) ( Fist Bumps Germs )