Your cat spends three minutes intensely scratching behind its ear, then looks directly at you with the expression of someone who's just discovered the problem was your fault all along. You reach for the flea treatment. It's been in the bathroom cabinet for six months. Your cat watches you walk back empty-handed and begins scratching again, this time slower, like it's filing a formal complaint. By the time you find it, she's moved on to judging you from the couch.