A chittering dolphin can sound like a bunch of monkeys jumping on a deflating rubber raft—trills, squeaks, whistles and clicks. These creatures have honed this cacophony over millions of years to survive in their watery world. Both dolphins and toothed whales can use the returning staccato from their highest-frequency clicks to echolocate, identifying the size, shape, direction and even speed of fleeing prey. But after decades of research, how exactly they produce these high-frequency noises remains unknown. And a group of scientists are pointing to snot as the ingredient that gives the cetaceans the extra oomph required to go ultrasonic. A dolphin’s staccato can clock in around 100 KHz—higher than a dog whistle. Even so, “you can’t make [the sound of] a dog whistle just by whistling,” says Aaron Thode, researcher at Scripps Institution of Oceanography, UC San Diego. But mix in a bit of snot and the situation could completely change. Dolphins make their noises with the use of a set of fat-filled strips called dorsal bursae located beneath the blowhole. This nasal cavity is sealed by a pair of lips that resemble and are commonly called “monkey lips,” explains Thode who presented the mucus hypothesis this week at the 171st Meeting of the Acoustical Society of America in Salt Lake City, Utah.