Well, the answer is quite simple and a little pathetic: the application I was using to draw the lab rats was accidentally closed while I was half-way through. As you can imagine, this caused much wailing and gnashing of teeth. Rather than starting all over again, I opted to simply clip and resize pictures I'd already drawn. Here are the originals:
An okapi.
A kangaroo.
A fox.
A rabbit.
Incidentally, the animals found in the left cheese are a fox, a Matschei's tree kangaroo, and a kangaroo possibly on LSD.