 Okay. So, how do erections work? How do... Oh, thank God, something finally useful in this lecture. How do erections... I just saw somebody pick up a pen for the first time this whole lecture. Okay. So, how do erections work? In order to appreciate that, we go back to exactly the nervous system component that Docker was talking about before the autonomic nervous system, sympathetic nervous system, parasympathetic, sympathetic, emergency, arousal, all help breaking, loose, adrenaline, stress response, parasympathetic, calm, vegetative function, big starchy meal, take a nap, working in opposition. Okay. Here's the rule. In order to get an erection, you've got to turn on the parasympathetic nervous system. You've got to be calm and vegetative. Okay. So, you got your erection. What happens next? Maybe something to do with the social context that brought about the erection in the first place. Maybe you start feeling a little bit less calm and vegetative. Maybe you start breathing a little bit faster. Maybe your heart rate increases. Maybe you're beginning to expend some muscular energy. Maybe you're beginning to turn on the sympathetic nervous system. And more time goes by and you're breathing faster and your heart's racing. And eventually, you know, your toes are curling and you're sweating and all of that. And you're like turning on the sympathetic nervous system throughout the whole body, except with this one lone outpost where you're desperately holding on to parasympathetic tone as long as possible. Finally, you can't take it anymore. You turn off the parasympathetic. You turn on the sympathetic and you ejaculate. Okay. So, that's how erections work. That's how erections work. And the question becomes what happens during stress? What happens during stress? You're not very calm and vegetative. You have trouble having an erection in the first place because you can't establish that parasympathetic tone. Or you can have a second problem. Suppose you do indeed manage to get an erection there, but you think, oh my god, global warming, something or other, you accelerate, you accelerate the transition from parasympathetic to sympathetic and the whole thing goes too quickly. Incredibly easy for this sort of erectile dysfunction to occur. Current estimates are 60% of the doctors visits in this country by men with erectile dysfunction. It turns out it is not organic. In basis, it is stress-related.