They are slow to reach certainty, open to discussing ideas that differ from their own, and willing to change their opinion in the face of evidence. They are not interested in gossiping about other people, but passionate about goals they wish to achieve.
By way of contrast, unintelligent people are relatively easy to identify. They tend to be dogmatic and reach certainty quickly. They tend to be very tribal in their willingness to buy into the beliefs of the fellow members of their group, and seldom differ in opinion from the consensus of the tribe to which they belong.
They change quickly. Average people don't want to get out of their comfort zone because they're afraid. Intelligent people get out of their comfort zone because they can easily adapt.