Sometimes a new and entirely different usecase is discovered for an already existing product. A good example of this is the pesticide Metaldehyde. This compound was originally developed as a solid fuel. It was only later discovered that it could also be used as a pesticide against snails.
Metaldehyde is used in snail pellets that also contain flour and molasses to make the pellet more attractive to snails. This concept was patented by Bayer AG and the patent has recently expired.
My question is whether it would also have been possible to patent metaldehyde itself as a slug pesticide.