erase wisely

this is from a webcomic called "brown sharpie". it's full of crazy math comics that i rarely understand, but occasionally there is one simple enough for me to laugh at. this is one of them. if you don't get it, act like you are erasing a chalkboard side-to-side, and think about what your butt is doing. i had a very few cute female teacher's aides in college, and this was the highlight of my recitations with them.