He can be taught

C went on his first trick or treat excursion this Halloween and quickly picked up the script. At every house, he said:

"Trick or treat. Happy Halloween. Thank you."

He became so used to the positive responses to this little speech that he received at each house that he stood staring at someone in a mask who didn't seem to be quite as enthusiastic as others had been. Not quite sure what C wanted, that person assumed (correctly) that a second handful of candy would be sufficient for whatever was worrying C.