I have looked up crowbar in a number of dictionaries of slang and

informal usage... and still have no idea what you just said.  Can you
reword it?

The point, I think, is that if pointer equality testing really does what
it says, then there shouldn't *be* any correct implementation in which
false positives are possible.  It seems the claim is that the garbage
collector might be moving things around, have just by chance happened to
place the second value in the spot formerly occupied by the first, and
have not updated the first pointer yet.  But if that's the case, and
it's executing arbitrary user code that may refer to that memory, then
the garbage collector contains race conditions!