We just finished graphing in my calculus class and spent Thursday reviewing for an exam. One of the kids was questioning concavity. I did my usual, explaining that concave up was like a happy face, you feel happy when you are up and concave down was the frown when you were sad. One kid said she remembered concave up because it began with a U like "up". We all agreed that was great. Another kid, a sweet, innocent (or so I thought) yelled out "concave up is like two legs in the air." Needless to say, we all started laughing. I don't know if I will ever be able to teach concavity again with a straight face.