Albert learns that his favourite joke might be a private one

Albert’s favourite joke is as follows.  Each day he attempts some sit-ups.  He can reach about twenty before he has to give up.

But if someone comes into the room during his brief exertions he always starts counting.

‘One hundred and twenty three,’ he says as he completes his fifth sit-up.  ‘One hundred and….twenty….four.’

Albert loves this joke so much he can sometimes laugh about it alone.