1. Timing of photo selection: If you see a photo of Suzy Bae in a photo or movie, her mouth may be open, because she is talking, laughing or expressing some emotion at this moment, so her mouth naturally opens.

2. Suzy Bae's mouth features: Everyone has different mouth features, and some people will open their mouths slightly when their facial expressions are natural. Therefore, Suzy Bae's mouth opening may be one of her personal mouth features.

3. Shooting angle and freeze-frame picture: Sometimes the choice of shooting angle, shooting method and freeze-frame picture of a photo or film will give people the illusion that the mouth seems to be open all the time, but it is actually just an instant picture.

Therefore, Suzy Bae's mouth opening may be caused by personal characteristics, shooting timing, shooting angle and other factors. These are just some possible reasons, and the specific reasons may require watching specific pictures or movies.