If nothing was unclear or difficult, say so. Skip questions about steps you did not experience; use not applicable where appropriate.

Which demonstration goal was unclear?
What prevented trying the activity?
What instruction would help?

Author notes / illustrative keys where applicable:
1. Use this answer to locate the part of the experience that needs explanation. The example issue to investigate is: visitors cannot tell whether they may use the equipment.
2. Barriers to trying a demonstration distinguish access instructions, capacity and prerequisite gaps. Explain the actual participation options before changing the activity; observation alone does not indicate whether the demonstrated task worked.
3. Turn the requested improvement into a testable next step. One illustrative action is: add a clear invitation and supervision guidance.