Further to this, I've found this excerpt from Richard Feynman's "Is Electricity Fire?" in
Surely You're Joking, Mr. Feynman!:
And then one day—I guess it was a Saturday—I want to go up in the elevator, and there's a guy standing near the elevator. The elevator comes, I go in, and he goes in with me. I say, "Which floor?" and my hand's ready to push one of the buttons.
"No, no!" he says, "I'm supposed to push the buttons for you."
"What?"
"Yes! The boys here can't push the buttons on Saturday, so I have to do it for them. You see, I'm not Jewish, so it's all right for me to push the buttons. I stand near the elevator, and they tell me what floor, and I push the button for them."
Well, this really bothered me, so I decided to trap the students in a logical discussion. I had been brought up in a Jewish home, so I knew the kind of nitpicking logic to use, and I thought, "Here's fun!"
My plan went like this: I'd start off by asking, "Is the Jewish viewpoint a viewpoint that any man can have? Because if it is not, then it's certainly not something that is truly valuable for humanity... yak, yak, yak." And then they would have to say, "Yes, the Jewish viewpoint is good for any man."
Then I would steer them around a little more by asking, "Is it ethical for a man to hire another man to do something which is unethical for him to do? Would you hire a man to rob for you, for instance?" And I keep working them into the channel, very slowly, and very carefully until I've got them—trapped!
And do you know what happened? They're rabbinical students, right? They were ten times better than I was! As soon as they saw I could put them in a hole, they went twist, turn, twist—I can't remember how—and they were free! I thought I had come up with an original idea—phooey! It had been discussed in the Talmud for ages! So they cleaned me up just as easy as pie—they got right out.