Okay, so what happens if a CAT accidentally ingests a maggot or fly egg? or if they get either on them:?

i'm cat sitting and when i went today i noticed that their food bowl for the canned food had still some food on it, which was odd because they usually have eaten it all by the next day, so i'm thinking maybe this means they noticed and chose not to eat it? but what if they did? or what if they ate some eggs?