If someone’s surprise lasts longer than a second or two, they’re likely to be faking their surprise.
Surprise is the briefest of emotions, with a sudden onset that dissipates quickly as the stimulus that caused the surprise is understood. Once the event that caused the surprise has been evaluated, another emotion quickly follows, such as happiness (a pleasant surprise), fear (a frightening event that was surprising), or disgust (discovering a dead rodent under some rubbish) etc. The only time surprise will continue for longer than a few seconds is when further surprising stimulus occurs, although technically this becomes a separate surprise event.
The appearance of surprise consists of three main parts: raised eyebrows, raised eyelids, and the dropping of the jaw.