Experimenters wanted to know the effects of smiling or frowning on the experience of emotion. To avoid problems with demand characteristics, the researchers had the participants in the experiment rate the funniness of cartoons while

A) viewing themselves in a distorted mirror.
B) holding a pen in their mouths, as a disabled person might.
C) their faces were numbed with a local anesthetic.
D) listening to a masking noise through a set of headphones.

Holding a pen in their mouths, as a disabled person might, would prevent the participants from using their facial muscles to make expressions of smiling or frowning, thus avoiding demand characteristics. This manipulation is known as the facial feedback hypothesis. Viewing themselves in a distorted mirror could still allow the participants to use their facial muscles to make expressions, and it may be less comfortable for some individuals. Numbing the face with a local anesthetic would eliminate the ability to make any facial expression, which may not be a realistic simulation of natural behavior. Listening to a masking noise through headphones would not have any impact on participants' ability to make facial expressions.