An involuntary clenching of the jaw, grinding of the teeth and slight pout of the lips that commonly occurs whilst stroking a cat.
Other side effects may include a high pitched baby voice and an overwhelming urge to squeeze the cat in question.
A 'kitty face' may also appear in other situations including; seeing a new born baby or washing a partner's hair.
Man: (to cat) Oh hello little puss puss, how lovely you look today. You have such nice fur, ooh I could just stroke you all day.
Woman: Darling leave that poor cat alone, you've got such a kitty face on.