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. 
He was never on his knees, always standing. 
mnli hypothesis: He was never on his knees, always standing.  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. 