A house fly eats solid food by vomiting on it first. If its food is a liquid it will suck it up and swallow it. If it is solid they need another approach. Flies don’t have any way to chew, so instead they will rub the solid food until it breaks into fine pieces and then vomit on it. Once the saliva and vomit mix has been on it for a few seconds, and started to dissolve, they suck it all up.