Originating from the spell "expecto patronum", as used in the Harry Potter novels. Used by both wizards and witches to fend off Dementors with a white shield of positive energy.
I just thought of something: you and I are part penguin and part llama. However, you can only have one patronus. Which one of us would have which patronus?? Guess we'll have to expecto patronum it up when you get home.