A drop of water falls from a bear onto the ground and needs to be wiped up with a towel. Only a teacher or an expert could get away with getting close to this wet bear to wipe up after it.
The teacher tells you to start with something smaller, after all, you're not an expert yet. You have to practice on a wet sheep (し). "I became a wet, dangerous animal expert by starting with sheep, you will too!" your teacher says.