A wandering eye indicates a lack of concentration. Especially if they look away or at other persons.
They'd prefer not to listen to you. If your surroundings are distracting, gently encourage them to concentrate.
Someone's hands might also show how carefully they're listening. Anxious and preoccupied people may fidget or interlock their fingers when not listening.
Those who aren't listening may beat their fingers on the table or rub their palms together. Boredom or thoughts may generate anxiety.
A person's body language might reveal how well they listen. Humans listen by turning towards the speaker.
Their general attitude, direction, and the angle of shoulder, face, and sometimes even feet are important indicators as to whether or not they are involved in the discussion.
Feeling like someone isn't listening is one of the top body language signs. Humans can usually perceive when they are being attuned or touched.
We feel distant when we don't feel sensed, which typically creates unhappiness.