Tai chi form was designed to train the body to move in an unorthodox manner that loosely emulates the combat postures used by a variety of animals.
These natural shapes are intended to be intimidating.

By mimicking the predatory movements and body shapes of animals, the human martial artist learns to shape their body language into something threatening during combat.
Many martial artists like to pull faces and exhibit aggressive emotional traits, but these actually inhibit clarity and impede judgement.
Employing the body language of animals is one thing, acting like an animal is something else entirely.

As the tai chi student becomes more skilful and adept, their body language gains an increasingly intimidating aspect during combat.
This promotes fear in the aggressor.