How do porcupines make love? Wendy Cooper discovered the answer while poking around the basement of the Australian National University library in Canberra about five years ago. Cooper is a parasitologist. She studies parasites, not porcupines. She also, in the course of her work, studies scientific journals. That was how she acquired her professional knowledge of porcupines' prickly procreation procedures.

Cooper found two studies written (one with co-authors) by Albert Shadle, of the University of Buffalo, New York, in 1946. Shadle was chairman of Buffalo's biology department from 1919 to 1953. One paper is called The Sex Reactions of Porcupines (erethizon d. dorsatum) Before and After Copulation. The other is Copulation in the Porcupine.

Wendy Cooper digested the information and published a summary, carefully worded to make sense both to porcupine specialists and to laypersons. From the outset, she is direct: "How do porcupines make love? You would probably think the answer is 'very carefully', but you would probably be wrong."

The porcupines in the study were part of a colony that Shadle kept at the University of Buffalo. The colony consisted of five females (Maudie, Nightie, Prickles, Snooks and Skeezix) and three males (Old Dad, Pinkie and Johnnie).

Come mating season, the scientists would place a male into a cage that already contained a female. Cooper described the subsequent action. First came courtship: "When the male encountered the female porcupine, he smelled her all over, then reared up on his hind legs ... If she was prepared for mating, she also reared up and faced the male, belly-to-belly. In this position, most males then sprayed the female with a strong stream of urine, soaking her from head to foot. She would 1) object vocally, 2) strike with her front paws, as though boxing, 3) threaten or try to bite, or 4) shake off the urine and run away. If ready for mating, the female did not object strongly to this shower."

Then the porcupines did the business: "The male made sexual contact from behind the female. The spines of both animals were relaxed and lay flat. His thrusts were of the 'usual nature' and were produced by flexing and straightening the knees. Males did not grasp the female in any way. Mating continued until the male was exhausted ... If males refused to co-operate, the female approached a nearby male and acted out the male role in coition with the uninvolved male."

This research project was potentially hazardous for the porcupines - and for the scientists. But a report written by Shadle late in his life offers perspective.

"The penetration of porcupine quills into the human body is never a pleasant sensation," Shadle wrote. "But 20 years of experience in working with a porcupine colony, and continued handling of these spiny animals, have convinced the author that description of the discomfort of being quilled is often very much exaggerated."

· Marc Abrahams is editor of the bimonthly magazine Annals of Improbable Research (www.improbable.com) and organiser of the Ig Nobel Prize