When the full moon rises, dogs and cats go wild -- and get hurt.

Dogs and cats suffering heart attacks, seizures and trauma end up at Colorado State University's Veterinary Medical Center emergency room in Fort Collins in higher numbers around the full moon, according to a study.

"We were dumbfounded when we actually saw the increase," said Raegan Wells, a Colorado State veterinary resident and primary author of a paper in a recent issue of Journal of the American Veterinary Medical Association.

It all started with people quipping "it must be a full moon" when the emergency room got busy, Wells said.

"We thought, 'Oh, this is nonsense. Let's just look at it once and for all and be done with it,'  " Wells said.

After reviewing records from 10 years and 12,000 animals, the researchers found that during the fullest 12 days in the moon's 28-day cycle, cat emergency visits were up 23 percent and dog visits up 28 percent.

"I'm skeptical that there's any true clinical application for our findings, and I don't know how to explain it," Wells said. One possible explanation is that cats spend more risky time outdoors, time hunting when the moon's light is bright enough for the felines to catch the twitch of a mouse's whiskers, Wells said.

But cat-trauma emergencies alone couldn't explain the spikes, Wells said; the increase wasn't statistically significant until all cat and dog emergency categories were included.

There also was no evidence of dogs behaving more aggressively during such lunar phases.

Pet owners might be more likely to hustle an animal in for emergency treatment when it's lighter outside, said Kevin Fitzgerald, a Denver veterinarian.