Ruth 3:8

‘ And it came about at midnight, that the man was fearful, and turned himself, and, behold, a woman lay at his feet.'

By this time it would be quite dark, and thus when Boaz awoke, and was conscious of someone lying at his feet he was a little apprehensive. Turning he noted that it was a woman. Not being able to tell who the woman was in the dimness it seemed to him quite out of place. Possibly the thought sprang though his mind that someone was trying to compromise him.