Who's the culprit?

I sat down at the computer, reached for the mouse and....eewwww!!  Someone used the mouse with nacho cheese Doritos encrusted fingers!!  I know it wasn't me and it wasn't Grant, so that leaves two suspects.  Both of them have been munching on the Doritos today and they are both capable of doing this deed.  I wonder if anyone will fess up?  Who do you think it was?  I'll keep you posted!