So tell testers they're on their own with the test scenarios. This just means they've helped find a spot where the Web site needs more work. As a usability tester works through the scenarios one by one, the observers should document the UI features applied to each task, noting any related usability issues. When you have more than one observer, consider assigning one the task of documenting the tester's emotional responses. A furled brow or wince can be revealing.
Some testers are quieter than others.
If necessary, the facilitator should ask questions occasionally to encourage testers to voice their thoughts on the usability of the site. Debriefing is an important part of the process. A facilitator halts the testing when it's time to debrief a tester. The debrief session lets the tester provide general feedback about the Web site and answer observers' questions. When many observers are involved, they should consolidate their questions and pass them to the facilitator.