A poor farmer has a pig but no boar, and wanting to breed the pig, approaches a neighbour who has a boar but no pigs.
They strike a bargain - the neighbour will allow the pig to be serviced by the boar once a week until the pig shows signs of bearing a litter, and he'll be able to choose two piglets after the birth.
The pig-owner has a tractor but it needs repair, so he loads the pig into a large wheelbarrow and trundles it up to his neighbour for its weekly servicing.
After four weeks with no result, he walks to the field where he expects to see the pig rooting about, but no pig in sight.
After searching fruitlessly all over his farm, looking for the pig or signs of a broken fence, he returns disconsolately to his barn, where he's amazed to find the pig lying in the wheelbarrow!