Weird, that — most flu viruses focus on the old and the weak, in true Darwinian fashion. But the 1918 flu tricked your immune system into attacking your own body. Maybe bird flu will too. That’s why I’m happy to remember that the last time I had a cold the damn thing lingered for three weeks. Clearly my immune system is no threat to anybody, and as an additional precaution my dislike of allegedly good-for-you foods like spinach and lettuce means I’ll never catch e. coli from a vegetable crisper.Since I’m supposed to get in the Thanksgiving spirit, I’ll mention how thankful I am to know that bad health habits came full circle and landed on the side of the angels this year. May your own vices prove equally profitable.