Justin Timberlake [1] proved he's pretty quick on his feet when he played the 5 Second Rule game on The Ellen DeGeneres Show [2] on Friday. After gushing about his "rad" son Silas [3], the singer went head to head with the host as they tried to come up with three quick answers to a series of questions asked by Mario Lopez. While Justin had an immediate response to how he's bringing sexy back, things got pretty awkward when he revealed that he keeps a bite guard in his bedside table. "I'm a grinder," he said with a smile. "I don't see nothing wrong with a little bump and grind." He also mentioned his famous ex Britney Spears [4] when Mario asked about his time on The Mickey Mouse Club. Watch it all go down in the video above.