Eggs - good Vs bad - how to tell?

[Postdog]

I remember something about eggs to do with them floating or sinking if they are good or bad, but I can't remember which is which. I just popped 2 in to boil and one did one thing, one did the other, so which will be the bad one?

[Beria]

if it floats its a bad one. same with witches.

[heathfield]

As Beria says. An egg with a large air sac inside might appear to be trying to float, but if any part of the egg touches the bottom of the pan, it should be OK.