New Bunny

A new rabbit came hopping in today, and frankly, I am very suspicious of this bunny. The rabbit won't supply a name, and I'm very suspicious it's because this bunny is a boy! Every other rabbit in the house is female, so you can imagine the disaster a boy bunny creeping in here would be. Does anyone have any suggestions for how to tell rabbit genders? This one isn't wearing earbows, which is usually what signifies a female rabbit.