How do you boil eggs?

[finn's mom]

I do it a different way, I let the water boil and then put the egg in, (prick it with a needle first) when it starts boiling again, I set the timer to 8 min. - that's how I like my "hard" boiled egg - on ryebread with mayonaise, salt and pepper.

I've done it that way, too...where I put the egg in after it's boiling. But, I think I've had to boil it for ten minutes after that, though...what does pricking the egg do?