• A Swiss man "is serving a four-year jail term after three poppy seeds from a bread roll he ate at Heathrow airport were found on his clothes."
• A 43-year-old Englishman who had a cigarette stuck to his shoe was sentenced was sentenced to four years in prison for possession of 0.003g of cannabis, which I would imagine is a microscopic amount.
• Customs officers held a woman for eight weeks before she was able to convince authorities that her codeine pills were prescribed by her doctor for back pain.
According to BBC article:
"If they find any amount - no matter how minute - it will be enough to attract a mandatory four-year prison sentence.Link
"What many travellers may not realise is that they can be deemed to be in possession of such banned substances if they can be detected in their urine or bloodstream, or even in tiny, trace amounts on their person."