Nom

A curious slug like creature that is able to eat pretty much anything and disolve it into nothingness. Particularly popular with criminals that wish to get into places that they are not supposed to be at or open things to which they do not have the key. Noms will devour absolutely anything and as their saliva are strongly acidic, they do not have trouble even with things that are made out of very durable metals or stone.
Some people debate whether this is an actual animal or maybe a monster or simply an alchemical or magical experiment that went wrong and managed to somehow escape and multiple after. But unlike classical monsters Noms have shown absolutely no interest in devouring living things, they do not like plants, nor bugs, no worms or even bigger animals. There was an account of a person who fell into what they thought was a puddle, but as they got stuck and could not actually get out of this thing on their own, they realised that their leg got stuck in a particularly large and well fed Nom, who was just sitting in the hole in the dirt, probably waiting for some dead leaves to fall from the sky to feed upon. The man was pulled up by two of his brothers and has sustained no injury (well maybe just a slight one upon his pride for getting stuck knee deep in a weird blue slug).
Nom's favourite food seems to be rotting things of any kind and they are able to devour those with lightning speed. They have started to be really popular aid in the castle kitchens to get rid of scraps and to determine if certain things that have the potential to spoil are still nice and edible or started to go foul based on how hungry the Noms react to it.