Marcello knew he could make his speech more effective by expressing emotion through gesturing and making certain facial expressions at the appropriate time. By doing so, Marcello was engaging in

Marcello was engaging in kinesics

Explanation:

It's the Analysis of nonverbal body interaction. e. g. stance, motion, gestures, facial expression, comportement of the eye. Kinesics is an understanding of the communication of body movement, like facial expressions and body language, nonverbal comportements related to motion of all or parts of the body.