The T. rex is the embodiment of ferocious: razor sharp teeth, claws and a taste for blood. If you were running away from one of these beasts, you might not even notice its tiny arms. But there they are, in every recreation, almost comically small arms. So what gives? Paleontologist Bhart-Anjan Bhullar sets us straight on this not-so-tiny question.

Do you have a head-scratcher you want us to answer? Unlike T. rex, you can scratch your head, and when you’re done, submit your Moment of Um question at