However, he went to the length of unbolting it, and opening and shutting it several times; this he did with the utmost precaution against making any noise. 
He worked with the door for five minutes, and tried not to make a sound.
mnli hypothesis: He worked with the door for five minutes, and tried not to make a sound. premise: However, he went to the length of unbolting it, and opening and shutting it several times; this he did with the utmost precaution against making any noise. 