I used to cut the mouldy bits off food and use it until I saw that program on decomposition the BBC did a few months ago where they said that the obviously mouldy bit is only the tip of the iceberg, in mould terms. Which put me right off.
A couple of weeks ago I got some OOD mozzarella out of the fridge: 'it'll be fine, it's in a sealed bag in brine' I said.
It was pink!
I threw it away.