Presumably she seasons her knickers with a good smear of fanny-batter and a skidmark or two before she offers them for sale, at £50 a pop.
Are they just a romantic keepsake of the layby liaison, do you think, or do they serve a particular purpose? Boiling them up and spraying the resultant liquid over the roses would wipe out any greenfly, I should think, and it may well make an effective, organic slug repellent.