A friendly firefighter passed this bit of wisdom along. I've yet to use it, but I trust this guy (despite the fact that he completely soaked me at work the other day by shaking the tree I was walking under. To prove that it was "raining." Bastard. I am still plotting my revenge - suggestions welcome.)
Anyway, should your child (or you, because honestly it's not just kids who are stupid sometimes, right) stick a finger, a toe, something in a hole from which he cannot extract it, douse the affected body part with Windex. Yes, Windex, not soap, not butter, not oil. Windex. Et voila, the body part should slide right out.
If you have occasion to use this method, please let me know, as I trust my firefighter friend, but you know, I can't throw him very far, so verification is always appreciated.