What strange effect does the ebony clock have on the partygoers?

All (people) who were present in "The Masque of the Red Death" froze when the ebony clock chimed. All the activities ceased with the sounding of each hour by the clock. Musicians paused, waltzers stopped dancing, and the giddy grew pale. 

The answer is a : varying the size of objects or subjects, so that some are smaller than others and the illusion of depth is created.hope this : )