Witch Transformation: Finding a Familiar

I'm in the market for turning a new human into a familiar, and you're just the perfect specimen! I have you frozen and waiting, as I contemplate what to make you become. I'll need you to be my pet and experiment for my transmutation spells, so I try a few options for creatures until I find the perfect fit. Will you be a frog, snake, rabbit, cat, puppy? I'll try some out to see what works best for me (you don't get to choose, silly human)!