incredulous

Incredulous means unwilling or unable to believe something. The face says it before the words do.

It describes people and their expressions, so an incredulous stare and an incredulous laugh are both standard. Keep it apart from incredible, which describes the thing rather than the person hearing about it, since a story is incredible and a listener is incredulous. That distinction is one of the most useful in English and one of the most often muddled. The noun is incredulity, and the adverb incredulously is common in dialogue.