What are some good questions to ask an applicant in a technical interview?

Something about there’s a penguin sitting on a block of ice creating a frictionless surface. If the penguin shoots a shotgun at a 35* angle to horizontal, does he move? How fast? How far?

I came up with a good one. I put together a few terminal blocks on a din rail. I’m going to ask him if he knows what it is/does and after if he can think of any ways to improve it. One of the little projects will be acquiring and performing all the engineering support to switching to screwless terminals to save assembly time.