If you’ve ever watched a frog enjoying a meal, you may have noticed him blinking again and again. Frogs don’t just blink when swallowing; they use their eyes to help them swallow their meal. A frog doesn’t chew up his meal and swallow, but forces his meal down in a series of gulps, using his feet, tongue and even his eyes in the process.
Frogs are carnivorous, chowing down on other critters like insects, small mammals, birds, snakes or even other frogs. Frogs do have teeth, but they don’t use them the same way as you do. A frog doesn’t take a bite, chew it up and swallow. Similar to snakes, a frog eats his meals whole, and usually while they’re still alive. He has teeth in his upper jaw called maxillary teeth, used for keeping a grip on his meal while he gulps it down.
Each time a frog swallows, his eyes close. The eyes depress down into the sockets to help move the food down his throat. He can swallow food without the assistance of his eyeballs, but being able to push the food significantly reduces the amount of swallowing he’ll need to eat his meal. He can close both eyes, or one at a time as needed to help force down food. His eyes don't do all the work. He’ll use his front legs to help force his prey into his mouth, and his tongue assists his eyes in pushing it towards his stomach.
At the University of Massachusetts Amherst, Robert Levine tested how frogs use their eyes to help them eat. Levine and his team tested leopard frogs and found out how many swallows it took for them to eat crickets with and without being able to depress their eyes. Levine found that when the frogs were unable to depress their eyes, it took 74 percent more swallows to completely consume their meal. The amount of swallows increased from about 2.3 swallows per cricket to 4 when they couldn't use their eyes in swallowing.
Blinking his eyes doesn’t just help him eat, it keeps his eyes safe. A frog eats his prey not only whole, but alive and kicking. A struggling snake could do some damage to a frog’s eyes. Shutting them with every swallow decreases the risk of the frog’s dinner hurting his eyes.