1 Steve: {teaching Care of Magical Creatures} Crikey, kids! Today, we're gonna learn how to shove yer arm down a croc's throat to force 'im to let go.
2 Steve: {showing off the croc next to him} The secret is to keep goin' until 'is fangs are up to your shoulder, then tickle 'is tonsils.
3 Hermione: But Professor Steve, they're still not magical creatures!
4 Steve: That's why I got ol' Flitwick to put a fire-breathin' charm on this one! Right, who's first?

2013-08-06 Rerun commentary: This is actually not an entirely spurious survival tip. If a crocodile has your arm in its mouth, your best bet is to reach in to the back of its throat and pry open the valve there which would normally be shut to prevent water flowing into the animal's lungs while its mouth is open. See WikiHow's guide to surviving a crocodile encounter, step 6. If you successfully open this valve, water will flood into the crocodile's throat, and its immediate instinct will be to let you go.

You're on your own if it's breathing fire, though.