Demo #1: Stop when done. Ask if they understood.

Ask what they want to see. Show just that, no more. Stop when done. Ask if they understood. 

Alternate (they just want to see the product, nothing in particular) : Depict a relevant scenario. Stop when done. Ask if they understood. (Need to have done research on them for relevant scenario.)

Ask them to think of a scenario. Get them talking. Don’t keep going.