The lock that can't be opened with a key.

[vov35]

I think that in picking, your side pin would press on the pick, and thus be pretty easy to simply push back and forget about.

[dls]

as i said it would be mushroom shaped to increase difficulty in putting it back the main reason for any spool pin etc in any lock is to delay the attacker. think of it like this, security causes delay, delay causes stress, stress causes mistakes, mistakes cause delay and so on