Frogs blink their eyes when they swallow their food because they don’t have teeth and blinking helps them get their food down.
This may not sound like an explanation on the face of it, but it is. Here’s how: a frog’s eyes, not unlike those of a hippopotamus, are bulgy, big, and located on the top of its head.
This helps it to see even when the rest of its body is submerged in water. It also means that the area inside the body that houses these big eyeballs has to be large.
When the frog swallows, it closes its eyes and pushes them down into their cavities, which are located at the back of the frog’s mouth. This movement helps to push the wiggling bug down its throat.
Since the frog’s tongue is better designed to shoot out and retrieve food than push it down into its stomach, this system isn’t a bad one.
And frankly, if we had to eat bugs, we’d probably close our eyes, too.