Hugh Hefner -- Chasing Tail at Playboy Mansion Wedding

Hugh Hefner or Crystal Harris's dog -- it's a toss up which one's sniffed more ass at the Playboy mansion ... but one of them took last night off, we presume, for the Harris-Hefner wedding.

Ex-Playmate Crystal forced her Cavalier King Charles Spaniel, named Charles, to go black tie for the ceremony ... which was attended by a small group of family and friends.

We're not much for wedding pics ... unless there's a damn cute dog involved.

So, there ya go.