Rats

Companies always test products on rats to see if the products are toxic. If the thing makes the rats hair fall out or gives them cancer, then the product is not going to make it to the human market. I think a pretty interesting side effect of this is that if humans go through a mass extinction due to some new food or perfume that is deadly to humans but was safe for rats, the rats will still be able to eat our dead bodies with no ill effect. Because after all, we never put anything in our bodies that would hurt a rat. While it might kill vultures or ants or the other things that normally scavenge on dead meat, the rats won't even lose hair or develop skin rashes from the poison. I'll bet rats get really excited by this possibility. Patience, rats, patience.