Poor fella - He thought he was just getting a standard physical before starting his job at Circe's Funhouse, and didn't think twice about drinking that small cup of 'medicine' - which was in reality Circe's powerful Bunny Elixir -

http://www.comus.tfcentral.com/elixirintro.htm

It had an immediate disorienting effect upon him, of course, followed by a slow growth of fur - and then, due to a quirk in his particular metabolism, a sudden and unexpected burst of transformation. The rest of his metamorphosis should proceed at a normal leisurely pace.