Apparently, the grunts have something to do with each pig's personality. The more the pigs oink, the happier they are, which means when they oink they are sort of saying "Thank you for feeding me and I am very happy with my house now." The study also revealed that those who make less noise are the grumpy ones.

Why do pigs pink?

During many years of reproduction, some genes are changed, causing the black pigment (eumelanin and pheomelanin) in pigs lose their function. This mutation (change in gene and lost function of pigments) results in the pink or white pig. Mutation to the black pigment is quite common among pigs.

Do pigs oink when they are happy?

happy pigs oink more! Animals' grunts and squeals help show off their personalities and how content they are in their pens. There's more to a pig's oink than meets the ear, with happier porkers making more noise than grumpy ones, scientists have found.