Observing users interact with a prototype can help understand its usability. Here are some key things to keep an eye out for:

• Intuitive use: Observe if users can naturally navigate the prototype without guidance. For example, do they struggle to find the Submit button in your app or is it obvious?
• Error frequency: Note how often and where users make errors, such as entering incorrect data in a form field.
• Non-verbal cues: Pay attention to body language and facial expressions for signs of confusion or frustration.
• Interaction duration: Measure how long it takes to complete tasks. Longer times may indicate usability issues.
• Workarounds: Notice if users create their own solutions, indicating a gap in your design.