Fish climbing trees! Good one, Jenni. Now I can't get the picture out of my head.
Our new cat finally discovered the vent below the cabinet in the kitchen. Cats love lying in the heat. It only took her a few days after that to connect the sound of the blower with the heat coming from the vent. When the furnace blower comes on, she will run upstairs and head straight for the vent. If the air conditioning is on and the blower comes on, she pays no attention to it. Maybe a slightly different sound because of the change in the air flow through the exchanger.
That type of behavior is what I would use to evaluate the intelligence of critters.