If one is fond of watching movies, then he/she must be familiar with the word 'trailer' of movies shown in cineplexes of shopping malls. Trailer is an excerpt or series of excerpts from a movie or program used to advertise it in advance. Thus understanding the word 'trail' becomes easier for trailer watchers.
After watching the movie and trailers of forthcoming movies, the viewer may enter the shopping portion of the mall and enter an apparel store. There are 'trial' rooms to try the clothes.
I have read that few girls visit malls, enter the trial room after picking the latest fashionable garments, wear that, take selfie and then post the same to their friends etc. Needless to mention here that they leave the clothes there only and come clean without buying anything.
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