Roger was on a train, mumbling to himself, smiling, and then raising his hand.
After a moment of silence, he would go through the same process … mumble, smile, raise hand, silence.
Maggie watched this closely, and after about ¼ an hour, she said, in a concerned voice, ‘Excuse me. Is anything the matter?'
'Oh, no,’ Roger answered. ‘It’s just that these long trips get very tedious so I tell myself jokes.'
'Why then', inquired Maggie, ‘do you keep raising your hand?’
‘Well,’ smiled Roger, ‘that’s to interrupt myself because I’ve heard that joke before.’