unconditioned
An unconditioned stimulus is something that is not usually associated with a certain response. For example, a bell might be an unconditioned stimulus, because it's usually associated with the sound of the bell being rung.
He couldn't get the dog to stop barking by using the usual methods, so he tried an unconditioned stimulus by throwing a treat in the dog's direction.
The student was not responding to the teacher's usual methods, so he tried an unconditioned stimulus by yelling at the student.