Are trolls smart?

When the 13 Drawfs and Bilbo get caught by the three trolls in the deep woods, they were going to get killed unless Gandolf didn't help them. Gandalf made it sound like one of the trolls were talking and they started arguing on how to kill the little people again. By doing this he distracted the trolls and safely got everyone free. The only reason that Gandalf was able to create another argument between the trolls is because he's a wizard and can easily manipulate the minds of the stupid, also it was dark and so it made it more easy to confuse the trolls. Trolls aren't smart because if they cant distinguish the difference between their own voices then they have to be unintelligent.