Example sentences:

Ramayana: When Rama approached Kaushalya to inform her that he had been exiled, he tried to maintain a deadpan expression; but with her mother’s heart, she immediately sensed that something was terribly wrong.

Mahabharata:  While Draupadi was being dishonored, no one in the assembly could stay deadpan; except for a few cheering supporters of Duryodhana, everyone else was horrified.

Bhagavad-gita:  The essence of being a spiritualist is not to live life with a deadpan face but to focus on the unchanging so that life’s changes don’t affect us too much.