Just had to smile to myself. I opened a new box of eggs (free range of course!) and with all the information on the lid it said "Allergy information: contains egg". I'd never have guessed!
I suppose it's because peanuts are strictly speaking not nuts, but I think they trigger off the same sort of allergies. I bought some frozen Yorkshire puds the other day and they packet said 'Does not contain nuts. Made in a nut-free environment. May contain traces of nuts.' Huh?