Watch the Entire Cast of The Big Bang Theory Passionately Make Out With Each Other

After hitting the 200-episode mark of their hit show this month, the entire cast of The Big Bang Theory sat down with Conan O'Brien on Wednesday night, when it was revealed that Mayim Bialik and Johnny Galecki go way, way back. Before they played Amy and Leonard on the popular CBS comedy, Mayim and Johnny hit it big as '90s child stars on the family sitcom Blossom. It was there they shared their first onscreen kiss, which Conan happily goads them into re-creating. As they lock lips once again, the rest of the cast joins in on the action, with even Kaley Cuoco grabbing Jim Parsons for a smooch! Watch the video above, and then check out Mayim's hilarious speech at the Critics' Choice Awards.