The student found the snail Wednesday on a salad served at the Kealakehe High School cafeteria. Principal Wilfred Murakami said the salad ingredients were washed properly by cafeteria staff.
"We drain it, strain it in a colander and go ahead and turn it into a salad," he said. "And in this particular case, one of the snails was lodged in one of the leaves."
Murakami said the lettuce brought in by a local vendor in recent days had more snails than usual, KHON-TV reported. He added he is taking the matter very seriously.
Snails and slugs can contain parasites that can attack the nervous system, causing rat lungworm disease. Hawaii state epidemiologist Sarah Park said the illness can be debilitating, taking months or years of rehabilitation to recover.
Officials at the Kailua-Kona school said they've notified the vendor, a local farm.
Murakami also said cafeteria staff will be more diligent in inspecting and cleaning the school's produce and other food "to make sure that none of these critters or insects get into it."