Fortunately, Bess doesn't catch frogs, but my 2 previous cockers, Teddy & Robin both used to catch them. Robin was the worst, we used to have a little pond in the garden. He would go out in the garden at night & catch frogs. He would hold one in his mouth (frog facing downwards!) until I went out & offered him cheese. Cheese was the only way to get a frog out of Robin's mouth. Most times the frog survived its vigorous sucking (at least I think they did, the following morning they were never where Robin had dropped them the night before!)
I don't know how many frogs he actually swallowed, but Robin never came to any harm, he lived to the ripe old age of 16.