Jake Gyllenhaal stopped by "Late Night with Seth Meyers" to chat about "Southpaw," where we learned some important things. Namely, that he did not make out with Seth Meyers' wife, even though they were friends for years before Meyers met her. Also, he has some tips for anyone in a fist fight, based on his experience playing a boxer in the film. Never talk during a fight, because getting hit in the head will make you feel like you're eating potato chips. Trust us, it makes sense when you hear him explain it. For all that and more, plus Meyers' secret role as Gyllenhaal's insanely ripped body double, watch the whole video below.