Questions that reveal what you would actually do

Ask what the last intern worked on and what happened to it. Ask who you would report to and how often you would speak. Ask whether there is a specific project waiting or whether it would be defined once you arrive. Ask whether the work gets reviewed.

The answers separate the two kinds quickly. "We will find something for you" is honest, and it means observation. A named project with a named supervisor and a review point means real work. None of these questions is rude — they signal that you intend to be useful, which is exactly what a good host wants to hear.