Mine was a chain. It was on my old yz 490, and the brand was "RK". It snapped.
I assume it was the master link. I installed new link, and it snapped again.
Being smart, and prepared, I had several links with me. By now, I was about 3/4 mad, and a total expert at chain repair.
One thing led to another, and the rear wheel rolled backwards, with good force. It trapped my index finger in the chain and sprocket. I was flexible enough to end up with my arm upside down, finger stuck, and it went clear to the chain guide. I had to roll the wheel forward to release the finger.
Smashed, broken, and cut. Filled with chain lube and dirt. I'll never forget the doctors curious look.
Somehow, I damaged a nerve as it happened, so it was almost painless.