He stood staring at the snails for a while, then grinned, looked up at me and started: ‘Have you heard the one about…?’ ‘Probably.’ I said.

‘No!’ he said. 'I mean the one about the snail who …’

‘Quite likely.’ I said.

'The snail who took off his shell …’ he persisted.

‘Definitely,’ I said.

‘Don’t spoil the punch line,’ he said and turned to his audience. His wife looked bored.

‘He took off his shell because he was feeling…’

‘Oh yes,’ I said. ‘I have heard that one… once or twice.’

‘Because he was feeling a little sluggish!’ He shouted flinging his arms out with a flourish.

‘Boom! Boom!’ said his wife.