A sandwich restaurant chain says it's looking into how a dead frog got into a customer's salad in Manhattan Monday.

The customer found the small frog in her salad from a Pret A Manger store on 47th Street and Sixth Avenue, according to her colleague Kathryn Lurie, who photographed it and posted it to the photo-sharing app Instagram.

Lurie, an editor at The Wall Street Journal, said on Twitter her co-worker wanted to remain anonymous but that "she was pretty shaken, understandably."

It's not clear how the frog got into the salad.

Pret said in a statement: "Our lettuce is sourced from farms that do not use any pesticides on its produce, therefore organic matter does very rarely manage to pass through our production process. We are currently looking into this issue to make every effort that this does not happen again."