A “cat” is used to help learn about squirrel reactions and their related sounds. (Courtesy of Robert Lishak)

Robert Lishak knows what the squirrels are saying.

What we may hear as nonsensical chattering the Auburn University biology professor perceives as the back and forth of squirrels communicating with one another — and with other animals, as well.

To study this squirrel talk, Lishak uses software that depicts the barks as jagged lines known as spectrograms and that show a sound’s duration and frequency. But scientists were studying squirrel sounds long before spectrograms became common, assembling a set of onomatopoeic words to describe unique calls: kuks and quaas, moans and muk-muks.

Lishak and his students spend hours in the field recording vocalizations and making observations. They even give squirrels something to talk about. They started out with a model of a cat that was pulled on a tether. Later, they trained domestic cats to hunt squirrels. (Don’t worry, squirrel-lovers. A monofilament line keeps the cats from actually catching one.)

Among their findings: Squirrels are observant. The way a cat moves through an area affects squirrel reaction. “If the cat is walking at an even pace, the squirrels ignore it,” Lishak said. “Stalking — starting, stopping — sets off alarm signals. If the cat makes eye contact, it sets them off in a New York minute.”

Squirrels are discerning, too. How are they able to distinguish between a harmless rabbit and a threatening cat, even from a perch high in the trees?

“It’s a pretty complex question,” Lishak said, and one he’s trying to answer.

For now, follow this guide and you, too, can speak like squirrels — or at least understand them.

Kuk — The kuk is a sharp bark of alarm, usually issued in a series: kuk kuk kuk!

“We used to think they were intended only for the ears of other squirrels,” Lishak said. But now researchers know there are two audiences for the kuk. The first is for conspecifics — a word that means others of the same species, i.e., other squirrels. “Rapid kuks say, ‘Hey, there’s a predator close by. This is imminent danger,’ ” Lishak said.

The second audience is the predator itself. Lishak’s work with trained cats shows that as soon as the squirrel starts kukking, the cat gives up, knowing it has lost the element of surprise.

Looked at on a spectrogram, kuks have a short duration and a broad frequency. Even if other squirrels can’t see their kukking compatriot, it’s easy for them to tell where the sound is coming from and thus where the danger is.

The squirrel also orients itself toward the threat. “The next time you hear kuks, look where the squirrel’s looking and you’ll see the reason,” Lishak said.

Quaa — The quaa is basically a long kuk issued after the threat level has dropped. It sounds a bit like a cat screeching. “A quaa says there is still danger — they can still see the predator — but it may be moving away,” Lishak said.

Quaa moan — This is lesser in intensity still. It sounds like a chirp followed by a meow.

The narrow frequency range of the quaa moan — and the way it starts softly, builds, then tapers off — makes it hard to tell exactly where the noise is coming from. It is, in the words of scientists, “ventrilocal.” Said Lishak: A quaa moan “means ‘I don’t see the predator. I think we’ve driven it from the area, but I better be as ventrilocal as I can.’ ”

For obvious reasons, the squirrel doesn’t want to give up its location.

Muk-muk — The muk-muk resembles a stifled sneeze: phfft, phfft. It’s quiet, only about 20 decibels, and is sometimes called a buzz. Nesting squirrels use it when they’re hungry and are attempting to solicit a feeding from their mother.

But the muk-muk does double duty. The next time you see a squirrel chasing another squirrel around a tree, listen for the muk-muk. The chase probably involves a male hoping to mate with a female. As he does so, the male makes the muk-muk. It means: Hey I’m chasing you, but I’m not a threat.

“To drive that home,” Lishak said, the male squirrel “produces the same solicitation call that babies give. It means: ‘Don’t fear me. I’m just looking to copulate.’ ”

It may not be a smooth pickup line for humans, but it seems to work for squirrels.

Join Robert Lishak and me Tuesday at 11 a.m. for an online chat. To post your questions about squirrels go to live.washingtonpost.com. To read previous columns by John Kelly, go to washingtonpost.com/johnkelly.