Why does my prayer get "better" when people are watching?

Sometimes I catch myself smoothing the prayer mat a little extra when I know someone will see me kneel. At taraweeh my hands linger on the carpet just long enough to make sure the row looks tidy. When my cousin is visiting from Dakar I say the words a touch louder. My grandmother used to pray quietly in the kitchen at fajr, her lips hardly moving, and I think of that when I realise my worship has become a performance. It scares me that I can measure my devotion by who is in the room. Has anyone else noticed this in themselves, and what did you do with that feeling?