>That doesn't mean that no one should ever ask questions like that. If the candidate explains that they can't think of the answer at the moment and why, and if the interviewer doesn't hold that against them (as long as the explanation is valid), then it's okay.

that's totally ok for me. that's why those are only two of the questions i usually ask, not all of them. i think saying "i don't know" is just as valid as any other thing.

as i mentioned elsewhere in this thread, these questions are "conversations starters" and the good data comes from the subsequent questions.

so if you said: "i can't come up with anything" i would probably ask about the last interesting project you worked on. or what was the last programming language you tried to learn.

interviews are not only for probing for tech knowledge, they are also about getting to learn about each other :)