They're fun to look at, but don't cross them!

Porcupines: Pretty cute, right? But they can also be pretty painful if you cross them.

In the clip above, PEOPLE Pet Vet Dr. Evan Antin of California’s Conejo Valley Veterinary Hospital hangs with two North American porcupines: Freddy, 8 months, and Walter, 16. The two live at the Wildlife Learning Center in Sylmar, California; Walter is the second-oldest porcupine to live in captivity, Antin says.

Though their quills define them, they also defend them: when threatened, porcupines shoot their quills at their foes — and Antin says it makes for some pretty gnarly vet visits.

To learn more about North American porcupines, watch Antin explain above!