"I jumped away," said 39-year-old Yvonne Brechbuhler, who described the green critter as no bigger than the tip of her pinky finger.
"I didn't know what it was. But once I realized it was a frog, I was OK," she told the Daily News in Thursday editions.
Intrigued, she named the frog "Curious."
Brechbuhler, a stage actress, said she bought the lettuce at her local food co-op and kept it in the refrigerator three days before using it last week.
Brechbuhler and her 7-year-old daughter, Orla, placed the frog in a jar on a bed of lettuce leaves and water, and fed it fruit flies they collected at a nearby garden. Afterward, they decided Curious would be happier at an animal facility specializing in reptiles and amphibians. The facility, Sean Casey Animal Rescue, has put it up for adoption.
An employee at the food co-op said it was the first such incident in memory.