The guard stops him and says, 'What's in the bags?'
'Sand' answers Mwangi.
The guard says, 'We'll just see about that.'
He takes the bags, empties them out to find nothing in them but sand. He detains Mwangi overnight and has the sand analysed, only to discover that there is nothing but pure sand in the bags. The guard releases Mwangi, puts the sand into new bags, lifts them onto the Mwangi's shoulders and lets him cross the border.
A week later the same thing happens. The guard does his examination and discovers the bags contain nothing but sand. He gives the sand back and Mwangi crosses the border on his bicycle.
This happens every day for three years.
Finally, Mwangi doesn't show up one day and the guard bumped into him in a cafe in Nairobi.
'Hey, buddy' says the guard, 'I know you're smuggling something and it's driving me crazy. Just between you and me, what are you smuggling?'
Mwangi sips his beer and says,
Spoiler:
