Leave it.

You eye the key for a moment, the chill taking flight up your spine again, then shake your head, as if answering someone else's question instead of our own internal one.

You stand, look around to see nothing has changed, then drop the key onto the sand again, turning to walk away.

You only get two steps, then think again and turn back. You hastily kick some sand over the object, then shake your head again, the chill finally going away.