A simple peasant is has bought a number of camels and is taking them to his farm. As he rides contentedly along he counts them - he counts 29. He was sure he had bought 30 camel, so in alarm he jumps off his camel and counts the camels again. To his delight there are 30. Half an hour later, he counts his camels and once more there are just 29. Confused, he climbs off his camel and counts again. Once more there are 30. Can you explain?
When he is on the camel he omits to count it.