'Mummy we get milk from cows' Heather announces.
'Yes' I say pleased.
'Mummy, we get eggs from chicken, don't we?'
'Yes' I agree, that's right.
Pleased that she was on a roll she continues - 'They do a poo and the egg comes out and we eat it.'
Not wanting to have to explain the finer techniques of egg laying I agree with her.
'Mummy,' she says after a pause 'Why doesn't an egg come out when I do a poo?'
At this point I gave up! Answers on a postcard...