Police are advised to take caution at restaurants after two deputies in Tampa, Fla., were served burgers containing shards of glass.

Two Hillsborough County sheriff’s deputies were in uniform on their dinner break at a 24-hour McDonald’s in Tampa. Deputy Stuart O’Shannon ate part of his cheeseburger and started coughing up blood. He was rushed to nearby St. Joseph’s Hospital, from which he was released the following morning. O’Shannon’s partner, Deputy Daniel Witt, was not injured.

Tiny bits of glass were found on O’Shannon’s and Witt’s burgers between a hamburger patty and cheese, hidden among similar-looking small pieces of onion.

The incident is under investigation. It is not yet clear if the hazardous burgers were intended for the deputies, nor whether the glass on the burgers was introduced by employees at the restaurant or at the food supplier, where the onions are packaged.