Is it usable? Can people figure out how to navigate through your product?
Are your calls-to-action visible? Do people notice the buttons or links that you want them to click on?
Are the steps to use a feature clear? Can someone figure out how to complete a task that you set them?
Is your copy clear? As people scan the words in your product, are they comprehending and moving forward smoothly? Or are they frowning and hesitating?
Is your product intimidating / jarring / confusing / threatening? As people are going through testing, is their body language indicating discomfort? (do they have furrowed brows, tense shoulders, are they fidgeting or hesitating, are they frowning)
You will not learn:
Is it useful? Would they bother if you weren’t there in the room watching them?
Are your calls-to-action compelling? Will people actually click them?
Do people understand what your features are? It doesn’t matter how ‘easy’ a feature is to use if people aren’t aware that the feature exists (or why they’d want to use it)
Is your copy convincing? When a person comes to your product with behavioral/purchase intent, do the words in your product help push them to action?
Why is your product intimidating / jarring / confusing / threatening? Because body language is at least partially subconscious, people may not notice that they are reacting to your product. Even if they do, they often can’t articulate what is bothering them or how it could be resolved.