"He literally is a genius... I always tell him, 'Darling, you know I'm going to have to give your mind to science after you've passed, because we're going to have to understand how all these sparks work.' We'll be in bed, and he'll be doing the crossword puzzle. Every night, he tries to finish it in under 10 minutes." Katy Perry gushes about her brainy boyfriend John Mayer.