I used to have one of these about 10" long. It was always very sharp. A co-worker from Trinidad, explained to me how when you step on a stingray they stick you with their barb. Naturally, from then on I was always afraid I'd step on a stringray.
That's why you do the "stingray shuffle" in waters where they live.
Stingrays are mostly shy and doscile creatures, however when threatened they will defend themselves with the spine.
When I was taking diving lessons, the instructor mentioned that if you're in waters where stingrays lurk, if you're entering from a beach, or walking on a sandy bottom, you NEVER walk. You shuffle your feel slowly. This will USUALLY get a burried stingray to move off. And you never swim close (an arms length) to the bottom. You can be on top of a burried stingray that has no way to move out. That could very well be how Steve got stuck in the chest.
Mark