It's small, but one of my favorite math professors in college, when he could tell the class was losing focus on the lecture, would begin proofs with a shouted "

It's small, but one of my favorite math professors in college, when he could tell the class was losing focus on the lecture, would begin proofs with a shouted "BEHOLD x!" instead of the more traditional "let x..." It always woke people up. Even for the most diligent students (which I was not), there will always be some dry material. Often, when I was struggling with writing up a difficult proof, I imagined him saying "BEHOLD," and it would cheer me up. Little things can make learning much more fun.