Breath of the Wild
"A giant organ obtained from a Molduga. This invaluable ingredient is hard to come by, and its use is shrouded in mystery."
Molduga Guts can be obtained by defeating Molduga, of which there are four exclusively found in the Gerudo Desert. This material can be used in combination with various Creatures to create different types of Elixirs, which increment Link's stats for a period of time, but can also be traded with Kilton, in his shop, the Fang and Bone, for 55 Mon each.
Age of Calamity
"A giant organ obtained from a Molduga. This invaluable ingredient is hard to come by, and its many uses are shrouded in mystery."
- Creating a Champion hints at the possibility that the guts are the Molduga's semicircular canals, though they actually resemble the cochlear apparatus more, both being part of the inner ear. The canals deal with XYZ-axis orientation, position and balance, and the cochlea transforms sound vibrations into electrical impulses. The guts being part of the Molduga's inner ear accounts for their importance in the creature's movement in its environment, as well as its behavior related to surface vibration within its territory.