In my experience, it is not uncommon for smaller live animals to be kept on hand and slaughtered freshly for each customer. Common critters are, of course, fish, lobsters and crabs, but also poultry, cats, small dogs (ever think of how the 'chow' dog got its name?), snakes and rodents. It all depends on the area and what the local delicacies are....

Contamination prevention? Uhhh....not so much. Except that they cook the meat.