why don't eggs from the fridge hatch?

[gumboil]

may seem a silly question but my young daughter wants to know why it is that eggs from the fridge don't hatch in to chickens.
she thinks that it can't be the cold alone that stops this happening as the eggs in shops are not sold from fridges.

[pleasehelpme]

i heard that if there is blood in the egg, it had been fertilised. howerver, prior to packaging, the eggs travel on a belt and are scanned by a powerful computer that checks for blood inside the egg. if a fertilised egg is detected, the computer system removes it from the belt.