When beluga whales want to communicate with each other, they just use the ol’ melon—a blubber-filled structure on their forehead. Researchers have found that the whales intentionally change the shape of the melon. That may convey different emotions or intentions—whether they want to play, mate, or just hang out.

Belugas live in and around the Arctic Ocean. They have a thick layer of blubber to protect them from the cold. And they don’t have a fin on their back, which allows them to easily glide below the ice.

They use their melon to send out pulses of sound, which helps them locate prey and predators and keep tabs on their fellow whales. They produce such a variety of sounds that they’re called “the canaries of the sea.”

Belugas are the only whales known to change the shape of the melon. Researchers studied what the shapes might mean. They spent a year observing two males and two females in an aquarium. And they followed up with shorter looks at more than 50 whales in a second location.

The scientists recorded more than 2500 melon shapes, which fit into five major categories. Almost all of the changes in shape took place when a beluga was around another whale. Many of the changes were associated with courtship, with males about three times more likely to make a change than females. But other changes were related to other social interactions, such as playing. So when a beluga has something to say, it just uses the ol’ melon.