I can’t recall exactly who, but every Thanksgiving, in the hazy afterglow of a full Turkey Day meal, one of my relatives says it. “Tryptophan must be short for ‘trip the light fantastic.’ ” It’s true; the land is always dotted with houses full of post-meal dopers, passed out from the effects of the serotonin-inducing enzyme lurking in tender, juicy slices of festive holiday poultry. It’s certainly not an unpleasant feeling, and it seems to do the trick even better than expensive prescription pills like Ambien. The tryptophan in turkey is for the most part nonhabit forming, won’t cause next-day headaches or thoughts of suicide, and of course, it’s all natural.