Hello there,
I was going to say. . ." Who cares, Just eat the darn sandwich, if you love your favorite sandwich, who care what happens to your elbow's. But anyways the correct answer is the fulcrum in your arm levers the joints in your body. This causes there to be a friction between the two muscles, causing your elbow to properly bend.
Hope this helps.
~Twizzie
And a little 'humor' is fine,Right! :D