This is an old one, but I heard it again today and decided to share it.

Q: What did one lab rat say to the other?
A: "I've got my scientist so well trained that every time I push the
buzzer, he brings me a snack."

Feel free to add other answers to this one!

Q: What did one lab rat say to the other?
A: "I wish they'd hurry up and knock FOXP2 into you too and then we could complete this conversation."

(NB FOXP2 is is the so-called “language gene,” as it plays a role in the neural development that is related to vocalization.)