Some one stepped on it. He rose from his knees, and walked slowly across to the mantelpiece, where he stood abstractedly fingering the ornaments, and straightening them, a trick of his when he was agitated. 
The it that someone stepped on was a glass.
mnli hypothesis: The it that someone stepped on was a glass. premise: Some one stepped on it. He rose from his knees, and walked slowly across to the mantelpiece, where he stood abstractedly fingering the ornaments, and straightening them, a trick of his when he was agitated. 