I generally agree you shouldn't ask pass/fail "trick" questions, but in most domains there are some questions that can tell you a lot more about someone than it might seem to an outside observer. For example, in an android domain interview, I've asked people to make a view blink onscreen. It's totally fine if they roll an implementation on the spot (and it's an easy question anyone can handle), but someone seasoned with the framework or who's read a lot of framework sources might know there's an undocumented feature of LayoutInflator that builds blink layouts if it encounters a <blink> tag while parsing layout xml. At least to me, that extra info is valuable. I'm sure there are analogs in for example C++ about quirks of the language that change with and without RTTI or exceptions etc that would tell you a lot about how much real experience someone has working with a given tool.