Researchers in a California biomechanics lab recently staged what should have been the most lopsided freshwater cage match of all time. In one corner was a red-bellied piranha, the razor-toothed terror of the Amazon. In the other was a three-striped cory, a faintly dopey-looking catfish about an inch long.

The piranha edged the cory into a corner, opened wide and chomped down once, twice, ultimately 10 times—only for the catfish to wriggle free and drift off unfazed, if a little miffed.

“It’s not even a startle response, where it’s swimming away fast,” says Misty Paig-Tran, an associate professor of biological sciences at California State University, Fullerton, with a chuckle of admiration. “It’s just kind of like, ‘What are you doing? Stop