Usability Testing with a Paper Prototype - Paper Prototyping: The Fast and Easy Way to Define and Refine User Interfaces - page 160

Answer questions when appropriate. Given that paper prototypes are often used before the
design is complete, sometimes the users raise really good questions that are outside the scope of
what you're testing. If the issue is an important one and isn't going to be covered by our tasks, I'll
simply answer it (or call upon the appropriate team member if I don't know the answer). For
example, in a security application used by network administrators, one of them wondered whether
the system would let them set the security level of the passwords created by end users ("Red Sox"
is easily guessable, at least in Boston; "Ab84gh" is not). This was something we hadn't planned to
cover, but it was an excellent question pertaining to functional requirements, so I let the product
manager discuss it briefly with the users.