"Mad handles" is a slang term originating in basketball, referring to someone having a truly impressive ability to handle the ball. It's also the first thing that came into my mind as I watched this adorable little otter play with a stone he'd found. He's got truly impressive skills, deftly rolling the rock around his arms and neck and just generally having a great time doing it.
According to user mickeysutube, who posted the video to YouTube, the action seen here is actually happening at half speed (i.e. he slowed down the video by half), which only makes the otter's feats more impressive. This otter lives at the Birmingham Nature Wildlife Reserve Centre in England, but it's clear to me that he's on a singular mission to put the "otter" in "Harlem Globetrotters."