Animals are frequently a challenge... after finding the right Animal Trainer with the right animal, you need to make sure that everyone is on the same page as far as what is expected from the animal.  What is the budget?  How many days of prep are needed?  You need to make sure that the director is happy with the performance,  you need to make sure that the actor has no allergies or is not squeamish when handling rats or spiders, you need to make sure that AHA is on board and that Locations knows what critters are going to show up.  No one is happy when 75 Brown Norwegian Rats show up and they are not mentioned on the permit or location agreement.