snort

To snort is to push air noisily out through your nose. Horses do it, and so do people who find something ridiculous.

The human version nearly always carries scorn, so snorting at a suggestion is dismissing it without words. It also happens involuntarily during laughter, which is a source of great embarrassment. As a noun a snort of derision is close to a fixed phrase. There is an informal drug sense meaning to inhale a powder. Horses snort as a genuine sign of contentment, which is the opposite of the human meaning.