 If you see a scene and the first time you crack up and you're laughing your butt off because you're with a bunch of friends and everybody's laughing and the thing that you see is the funniest thing you've ever seen. You can see it a week later and not laugh at all. And that's because the hormonal balance in your brain is telling you whether to be joyful and think something's funny or whether to, you know, not. Or, you know, falling in love is a...