AMPHIBIAN WARNING

The sexual innuendoes in this tale can't be overlooked:

Simple Boy—Sent to School—Learns Language of Frogs —Hero Exposed— Second Adventure on Road - Frog Restores Host to Sick Girl 

The story goes like this:

So Jack's father sent him to school for another year, and when he came back he asked him what he had learnt.

"Well, father," said the boy, "when frogs croak I know what they mean."

"You must learn more than that," said the father, and sent him once more to school.

Thereupon the father grew very angry at Jack and his love for him changed to hatred, and one day he spoke to a robber and promised him much money if he would take Jack away into the forest and kill him there and bring back his heart to show that he had done what he had promised. But instead of doing this the robber told Jack all about it and advised him to flee away, while the robber took back to Jack's father the heart of a deer saying that it was Jack's. Then Jack travelled on and on, and he found a companion in the lordling of the first castle he visited.

Soon afterwards they arrived at another castle in which the lord's daughter was lying sick unto death; and a great reward had been offered to him that should cure her. Now Jack had been listening to the frogs as they were croaking in the moat which surrounded the castle. So Jack went to the lord of the castle and said, "I know what ails your daughter."

"What is it," asked the lord.

"She has dropped the holy wafer from her mouth and it has been swallowed by one of the frogs in the moat."

"How do you know that?" said the lord.

"I heard the frogs say so."

At first the lord would not believe it; but in order to save his daughter's life he got Jack to point out the frog who was boasting of what he had swallowed, and, catching it, found what Jack had said was true. The frog was caught and killed, the wafer got back, and the girl recovered. So the lord gave Jack the reward which was promised, and he went on further with his companion and with another guest of the castle who had heard what Jack had said and done.

And his comrades at first laughed at him, but then remembered that what he had said before of the croaking of frogs had turned out to be true.

A German analysis points out: Der junge Held bestreitet nun mit Hilfe der Tiere bzw. seiner Tiersprachenkenntnis verschiedene Abenteuer, in denen jeweils nur er helfen oder heilen kann: eine kranke Prinzessin heilen...

Französisch: "Le langage des bêtes". Hier melden die Frösche, dass ein Mädchen erkrankt ist, weil es die Hostie fortgeworfen hat.

In some versions, the damsel has actually got the frog, or a snake, inside her, and the hero performs a form of exorcism:

Die Erd- und Mondgöttin erscheint in einer Variante des Märchens noch in einer isolierten Gestalt einer Prinzessin, die eine Kröte (Schlange) im Körper (Schoss) trägt, was die häufig vorkommende Kröte in diesem so scheinbar männlichen Zaubermärchen enträtselt.

SEXUAL METAPHORS, ANYONE?

• Exvotes for uterine complaints had a distinctive frog shape.
• Amphibians: metamorphosis with change of environment
• Ailing princesses in folktales tend to suffer from ennui or lovesickness, if not demonic possession
• Wafer / Host: flesh of Christ, part of the Eucharist together with wine/blood
• the damsel fell ill because she dropped the wafer
• a frog ate the wafer
• once the frog is killed and opened, the damsel consumes the wafer, which heals her
• legends about young females (ALWAYS young females) impregnated by swallowing (usually, drinking water), then birthing octopi, frogs, snakes... (compare Katharina Geisslein) are still common: http://www.snopes.com/pregnant/octopus.asp 
• (The sci-fi film Alien, with its male "pregnant" host, stands apart as a twist on the old formula)