Anemone will eat anything that falls in. A piece where people get into trouble, as they think the photosynthetic anemones need to eat, and end up feeding much too large piece of food. It ends up being stressful and counterproductive, as usually what we try to feed an anemone doesn't provide as much energy for them as what it takes for them to actually digest the food.
The other reason anemone have issues with their mouths is stress. When stressed they will 'vomit' up their insides, open their mouths to indicate stress, and other such things. Might be that we are in this territory. But color and extension looks good. Have there been any changes recently? How long have you had it? Can you tell us more about what is going on in the system?
