A seven-year-old polar bear named Baffin was killed at a Canadian zoo after another polar bear crushed his throat while playing. The incident happened Friday at the Calgary Zoo, and the Daily Mail reports that zoo visitors were looking on when the death occurred. According to the outlet, eight-year-old Siku was play-fighting with Baffin in a lower pool in their enclosure when he bit Baffin’s trachea. Baffin then sank to the bottom of the pool, and when he didn’t come back up, visitors became alarmed. After Siku was removed and the pool was drained, Baffin’s body was found. A necropsy revealed that while Siku’s bite didn’t break the skin, it did significant damage. Sandie Black, a veterinarian at the zoo, hypothesized that Baffin “lost consciousness underwater due to the tracheal injury and subsequently drowned.” “Had this been on land, it would have been very different,” Black added. A Facebook condolence post from the zoo said they “were mourning this loss deeply.”