In addition to the moderator, it is always useful to have one or more observers to take notes. These notes could describe how the participant reacted at certain points, take note of anything unusual that occurred, and identify interesting points during the test to review on the recording. Different observers may draw different conclusions, so of course it is best to write notes that describe rather than interpret.
You may have other observers watch the test, although its best that they remain in the background so as not to overwhelm the tester. Observing a usability test is a useful way to engage product managers, clients, stakeholders, and others, and let them see firsthand how people are succeeding or struggling with the product.
The Note-taker Role:
Take observational notes. Keep your observations separate from any overall insights or design solutions.
If you don’t have a note-taker, you can refer back to a recording. Don’t try to keep focus on your test subject and take extensive notes at the same time.
You won’t necessarily know something is important until you look for trends across the results of all tests.