An underwater microphone has picked up two dolphins seemingly carrying on a conversation as if they were two people, the Telegraph reports.

When researchers in Russia recorded a pair of Black Sea Bottlenose dolphins in a pool, it sounded as if they were chatting—and quite politely, at that.

Each dolphin would listen to the other without interruption before responding. While researchers have known for a while that dolphins could communicate via clicks or whistles, this study found that they also altered the frequency and volume of their sounds.

As a result, researchers say the aquatic duo could form sentences of up to five "words," though scientists had no idea what they were going on about.

The dolphins` communication skills exhibit "all the design features present in the human spoken language," writes lead researcher Vyacheslav Ryabov in the journal Mathematics and Physics.

"Their language can be ostensibly considered a highly developed spoken language." Now, says Ryabov, it is up to humans to decode dolphin speak. Their high-frequency sounds are beyond the human range of hearing, notes the Christian Science Monitor, but scientists could use equipment to capture and mimic those sounds, then respond in a way the dolphins would theoretically understand.

Australian researchers have previously pinpointed particular whistles the mammals use to communicate ideas such as, "There`s food over here," per the Telegraph. (Last year, scientists using 3D imaging figured out how dolphins "see" with sound.)