With Mercury in Aquarius, they express themselves easily, usually have a good memory and like to investigate the why and the what-for of things. At times they seem like a little encyclopedia: they use specialized vocabulary or talk about subjects others find unusual.
They choose carefully whom they relate to. If they feel a conversation lacks the level or interest they are looking for, they may fall silent and withdraw mentally. Outside specialized, intellectual or professional settings, that attitude may be perceived as lack of interest or of sociability.
Sometimes they argue for the pleasure of exploring ideas more than out of a wish to convince. Yet their questions or gestures can make another person feel ignorant. They may not notice that effect because they are focused on the precision of the subject and on their own curiosity.
The simplest question may get an answer of university-lecture length. When they find someone they respect, they enjoy conversing and may enjoy teaching. That confidence can also live alongside the humility to learn, to acknowledge a mistake or to admit they do not know something.