I went to a Mexican restaurant a couple of weeks ago. The weather was nice, so I took my plate outside to a table on the patio. Before long a half dozen birds were hopping around me on the patio. I broke off some tiny bits of tortilla chips and tossed them into a dirt planter next to the patio. The birds raced to grab the chips. (The rule among birds seems to be: if another bird already has food in its beak, don't harass it. But if it carelessly drops the food from its beak, it's fair game and the race is on.) Then I flicked an equally tiny piece of pollo (Spanish for "chicken") into the planter. The birds all started toward it, but when they got to within a couple of feet, they stopped in their tracks and looked at me as if to say: "Hey, we ain't a bunch of cannibals, you know." This brings to mind a couple of questions. (1) How do they know that the piece of tortilla chip is good for them? Does it smell like the corn that it was derived from? It surely doesn't look like any sort of food they would find out in a farm field or whatever. Maybe it's just a matter of experience, in that they have seen it enough times on the restaurant grounds to become familiar with it? (2) How do they tell that the bit of chicken was not something good for them? I mean, without actually getting close enough to get a really sharp look at it or picking it up in their beaks and giving it a taste test?