The parallel between  the animals chosen to represent generative or transitional elements in the underworld is intriguing. The Mayans used the snail; Bosch used a frog.

Both are small, slimy, amphibian creatures, that is, creatures that mark a transition between solid earth and water. This relationship cannot be coincidental.

Furthermore, the animals are edible.  Although the lower elements that make up the mind of man, both his conscious and unconscious manifestations, represent a corruption of the divine influence, they can and need to be eaten — ingested, and made a part of oneself. The paradoxes that arise here are, perhaps, self evident. Yet the understanding of the lower and corrupted material world as a necessary element to feed the spiritual being is consistent in both iconographies.