Bowl of what?

So I go to the Renaissance festival last year and they have a show with various birds from all over the world. One of these birds they show is the african vulture that can de-bone a chicken leg while being held by a trainer in 5 seconds. Very impressive. Ill bet in the wild that situation occurs everyday. So in telling us the virtue of the bird, the trainer guy says the immune system of the bird is so strong it can eat a bowl of anthrax and survive. Interesting. But my question is obvious, how in the hell did they find that out? Did the trainer happen to have a bunch of vultures at one time and then they got into his stash of anthrax and only one lived, having only eaten a bowl full? Or was he experimenting with how much anthrax it would take to kill a vulture, and a teaspoon wasn't enough, a bucket was too much, but a bowl was just right. Maybe the vulture ran out of food one day, and the only thing the trainer had left was anthrax, and he liked it. Does the trainer sprinkle anthrax on the chicken leg for the bird before he feeds it to him? Kinda like salt? Does he have like a petting zoo situation for the bird, and kids can give it little cubes of anthrax to eat, just no more than a bowl full?