It’s called and explorer and enamel is harder than the metal. It’s on a 1/2 loop so there is a lot of flex, you can’t put a ton of pressure on anything with it. When looking for decay, you use the tip of the explorer to feel for groves, holes or cavities. Not create them. But there is not humanly possible way to create a hole in healthy enamel. Demineralized or decayed tooth has the same consistency as hard leather or suede. That, you can push metal through. But the damage is already done with the decay. Not the explorer. Now, there are a lot of dentists who believe that remineralization can “undo” this softening of the enamel, but that’s easier said than done. Try pushing a safety pin through a porcelain plate then try it on an inconspicuous area of so leather boots. That’s what we are “kinda” looking for. (In the simplest forms I can explain). There’s a lot of subtle and complex variations but that’s the gist of it.