Something in the sack wiggles.

David Sever pauses, picks it up and begins to wrench open the knot, complaining that he tied it too tightly. He adds, however, that good knots help to keep reptiles from escaping in his vehicle.

Knot loosened, a snake — tongue flicking — pokes its head through the opening.

As Sever talks about the beauty of the green reptile with its black spots, he gently lifts it from the sack.

The snake, one of a variety known for eating other snakes, wraps around Sever’s arm and appears to be unafraid of the man who found him that morning and slipped him into a sack.

The snake moves up his arm while the Southeastern Louisiana University herpetologist talks about how king snakes range from the East Coast to the West Coast and from Canada to Mexico.

Sever and Robert D. Aldridge, of St. Louis University, recently co-edited a new book called “Reproductive Biology and Phylogeny of Snakes.”

Among its 17 chapters are some authored or co-authored by Sever, SLU biologists Brian Crother and Mary E. White, and graduate student Justin L. Rheubert.

Written mainly for scientists and advanced biology students, Sever said others with an interest in snakes can “find much to learn from it.”

It contains chapters on the evolution of snakes, which date to dinosaur times and now have an “incredible diversity” of about 3,000 species, Sever says.

Sever and his students have traveled around the world to study many of those species.

One of his students just returned from Costa Rica with a number of sea snakes for a study on their reproductive organs, which appear to be somewhat different than other snakes SLU scientists have studied using electron microscopy.

Another of Sever’s graduate students is laboriously slicing up a python to determine more about its reproductive parts.

Many of the snakes Sever has caught and studied since coming to Louisiana have been cotton mouth moccasins.

When studying snakes, a large sample size is needed. Sever said that makes the cotton mouth a perfect snake to study in Louisiana because he not only can find lots of them, he also can locate one any month of the year.

Though bitten numerous times by nonpoisonous reptiles, Sever said, he’s never been bitten by a cotton mouth or other venomous snake.

After putting the king snake back in the sack, Sever moves to another area of the biology building where he provides water for a couple of large copperheads. Before he gives them the water, he moves them with a grabbing device that keeps his body out of their reach.

“We used to catch them by hand,” he said of snakes used for research.

Sever caught and first became interested in snakes much like any other little boy might.

He and his older brother captured a garter snake as part of his brother’s work to obtain a Boy Scout merit badge.

Later, Sever and his friends would go out and catch snakes for fun.

As evidenced by the king snake in the sack, Sever still likes to catch snakes.

The herpetologist said that later in the day, he planned to let the long, slender snake loose in his backyard.