If someone vomited on your food and then proceeded to suck the vomit back up, you might be more than slightly disgusted. However, that’s how certain  fly species dine – they rely on digestive juices in their vomit to dissolve whatever it is they want to eat, because their mouths lack the ability to bite or chew; those juices liquefy their food for them. Because they also land on some unsavory and downright unhygienic foodstuffs for dinner, these flies are classified as pests.  

[Animalia > Arthropoda > Insecta > Diptera > Muscidae, Calliphoridae, etc.]