Her zygomaticus muscle stands out when she laughs.

He often whistles using his buccinator.

By training the frontalis muscle, your facial expressions will become more expressive.

He exercises every day to strengthen his risorius muscle.

He goes to the gym every day to train his thigh muscles.

When the arrector pili muscles contract, goosebumps occur.

The cold caused my arrector pili muscles to contract, giving me goosebumps.

Training the respiratory muscles is very important for aiding breathing.

Smooth muscles contract spontaneously and control many internal movements of the body.

It's important to train your antagonist muscles as well when doing muscle training.