'Ow!' shouted the victim and then, to the surprise of all concerned, he added: 'Hahahaha!'

'What you did was - sorry to impose again, sir, this won't take a minute - what you did was this—'

'Ow! Hahahaha!'

'Now, you lot, you saw that? Come on, gather round...'

Half a dozen other youths slouched out of the alleyway and formed a ragged audience around Mr Boggis, the luckless student and the victim, who was staggering in a circle and making little 'oomph oomph' sounds but still, for some reason, apparently enjoying himself immensely.

'Now,' said Mr Boggis, with the air of an old skilled craftsman imparting his professional expertise to an ungrateful posterity, 'when inconveniencing a customer from your basic alley entrance, the correct procedure is - Oh, hello, Mr Ridcully, didn't see you there.'

The Archchancellor gave him a friendly nod.

'Don't mind us, Mr Boggis. Thieves' Guild training, is it?'

Boggis rolled his eyes.

'Dunno what they teaches 'em at school,' he said. 'It's jus' nothing but reading and writing all the time. When I was a lad school was where you learned somethin' useful. Right - you, Wilkins, stop that giggling, you have a go, excuse us just another moment, sir—'

'Ow!'

'Nononononono! My old granny could do better than that! Now look, you steps up trimly, places one hand on his shoulder here, for control... go on, you do it... and then smartly—'

'Ow!'

'All right, can anyone tell me what he was doing wrong?'

The figure crawled away unnoticed, except by the wizards, while Mr Boggis was demonstrating the finer points of head percussion on Wilkins.

It staggered to his feet and plunged on along the road, still moving like one hypnotized.