Why would a dog repeatedly bury live frogs?

The following story was published in Dog Stories From The Spectator : Being Anecdotes Of The Intelligence, Reasoning Power, Affection And Sympathy Of Dogs, Selected From The Correspondence Columns Of The Spectator by J St Loe Strachey (1895):

[Feb. 2, 1895.] I venture to send you the following story I have lately heard from an eye-witness, and to ask whether you or any of your readers can throw any light upon the dog’s probable object. The dog in question was a Scotch terrier. He was one day observed to appear from a corner of the garden carrying in his mouth, very gently and tenderly, a live frog. He proceeded to lay the frog down upon a flower-bed, and at once began to dig a hole in the earth, keeping one eye upon the frog to see that it did not escape. If it went more than a few feet from him, he fetched it back, and then continued his work. Having dug the hole a certain depth, he then laid the frog, still alive, at the bottom of it, and promptly scratched the loose earth back into the hole, and friend froggy was buried alive! The dog then went off to the corner of the garden, and returned with another frog, which he treated in the same way. This occurred on more than one occasion; in fact, as often as he could find frogs he occupied himself in burying them alive.

The rest of the 1895 story, and one possible explanation, is at The Public Domain Review.