Frogs don’t have teeth, so blinking when they swallow helps them get their food down.
Frogs’ eyes, not unlike those of the hippopotamus, are big, bulgy, and located on the tops of their heads. This helps them to see, even when their bodies are submerged in water.
The problem is that it also means these huge eyeballs take up a lot of space inside the frog’s head. When the frog closes its eyes to swallow, the lids push them into the back of the frog’s mouth, helping to force the wiggling bug down its throat.
Since their tongues are better designed to shoot out and retrieve food than to push food into their stomachs, this system isn’t a bad one.
And frankly, if we had to eat bugs, we’d probably close our eyes, too.