Years ago, I had a little duffer bite my fin. We had a bit of a tug of war and he eventually let go. I didn't see him coming nor what caused him to bite my fin. Just glad it was my fin even if he was under 2 feet.
Only 5 or so years ago, our group was being shadowed by a cuda. Of course, I assumed it was going to be that normal swimming along business. At one point, the group was looking back at something behind me but I was swimming forward. I saw the cuda swing around and start to speed up straight for the head of a young female diver. The guide was next to her. No one else noticed. I was pointing and kicking as fast as I could. Finally, the guide noticed my behaviour snd started to turn his head. Out of the corner of his eye, he saw the cuda and mere inches from her head, batted it away by bringing up his arm fast to protect her. Fortunately, the cuda backed off and stayed backed off.
Neither the guide nor I could figure out what caused that behavior.
The young woman had dark hair, a full suit and was not wear jewelry.
In a completely different set of circumstances, some folk were on their way out to so a night dive and one of the divers stuck his mask and whole hand in to the water to rinse his mask. He was struck then. No one was positive that it was a cuda but determined that made the most sense. He ended up in hospital in Manado and his dive trip was over before it had begun.