Graham Martin, who works for Berkshire Reptile Rescue, was called in to consult on an odd case plaguing a Waitrose distribution center in Bracknell, England. As Martin told BBC ... he was tapped to collect a live toad from the business after it had been discovered inside a bag of salad.

Apparently, the surprise addition to the pre-packaged greens was first detected by a customer, who had purchased the item. It was reportedly returned after the live amphibian was spotted inside the bag.

The toad -- whose origins remain unknown -- is currently in Martin's custody ... who assured others that the creature was being well taken care of.

He added ... "He is in a nice little box, he's got some soil and some leaves to hide in, he's got a little water bowl. I've chucked in some beetles for his dinner and he's loving life."

Martin explained the toad was being kept isolated as "interaction with foreign animals is never a good idea."

A spokesperson for John Lewis Partnership, the company that owns Waitrose, made it clear this should never have happened ... given the fact there's "a stringent sorting and washing process which should have removed this toad."

The company also apologized to the customer who found the toad in their salad bag.

While JLP tried to downplay the situation as a "very rare occurrence," Martin said he's already had "3 or 4" calls this year about rogue critters finding themselves where they shouldn't be.