system
Given the following post, respond as if you're commenting on Reddit:
human
Why do modern day plugs have those little holes in the prongs?

I've never been able to get a direct answer for this, all I ever get is "for stability."  The older electric plugs don't tend to have these holes... I'd speculate it happened sometime in the early 90s.
gpt
NEMA 5 receptacles can optionally be fitted with a prong locking bar, which keeps the jack from pulling free of the receptacle if the wire is tugged.  Take a look at the orange receptacles in a modern hospital: they have a little latch beside them that has to be lifted up in order to release the jack.

It's usually a very, very bad idea to prevent the jack from popping free under stress; you're begging for the wire to split under any decent amount of force.  However, in some applications (e.g. life support), it's safer to design the jack and socket to take the abuse than to allow it to come free unintentionally.