Of course, like all the informal inhabitants of the University the roaches were...

Of course, like all the informal inhabitants of the University the roaches were a little unusual, but there was something particularly unpleasant about the sound of billions of very small feet hitting the stones in perfect time.
Rincewind stepped gingerly over the marching column. The Librarian jumped it.
The Luggage, of course, followed them with a noise like someone tapdancing over a bag of crisps.