What cut into a teenager in the ocean off Sunset Beach just south of the iconic restaurant Gladstones is still under debate.
But a marine biology major who became a surgeon says a great white shark is responsible even though lifeguards said there was no shark sighting before, during or after the incident.
Up until a few hours ago, Sophia Raab only knew she was severely injured surfing.
The 18 year old from Santa Monica hit the water off Pacific Palisades Wednesday with a friend.
But suddenly the shoreline around her turned red with blood.
"I had no idea," she said. "I thought I was going to lose my leg."
Lifeguards, fellow surfers and a friend came to her aid.
But it wasn't immediately clear what happened. Could she have been struck by the back fin of her surfboard?
Raab Googled orthopedic surgeons and found Dr. Bert Mandelbaum, who is convinced it's a great white.
"It's a shark bite by a great white or a mako," he said. "Probably three to four inches."
Mandelbaum also happens to be a former lifeguard who frequently swims with the sharks.
"I know my sharks," he said. "This is my first bite, but it's a bite."
Los Angeles County lifeguards say there was no shark sighting before, during or after the incident.