There were no footmarks.'
'Meaning that you saw none?'
'I assure you, sir, that there were none.'
'My good Hopkins, I have investigated many crimes, but I have never yet seen one which was committed by a flying creature. As long as the criminal remains upon two legs so long must there be some indentation, some abrasion, some trifling displacement which can be detected by the scientific searcher.

Autor: Arthur Conan Doyle