A snack is assigned a devil face when there is no nutritional value to eating it. These snacks are junk food with nothing in them to sustain the body. These foods are considered "empty calories".
Sometimes, we choose to assign a devil face when the caloric cost of eating the food outweighs any nutritional benefit from eating it. For example, you would get protein from eating beef jerky, but for 260 calories and lots of chemicals is a high cost to pay.
All snacks with a Devil Face