Trailer analysis - Unfriended

The beginning of the trailer starts off really happy and supportive. People are graduating, smiling and then the music and the pace of the trailer change. It becomes more dark and more eerie. The trailer then shows some embarrassing, regretting decisions through a video. We learn that these embarrassing videos and photos are of a girl called Laura and that she has died. Her group of friends have a Skype call but an unknown person trys to get into the call and succeeds. This is a clever way to introduce the killer as we don't know their identity. There is no picture or name and we don't even get to see the person at all. This becomes scary because every teenager can relate to having social media. Also the fear of the location, they are all in their individual houses yet, the killer is effecting all of them at the same time, whist they are on their skype call.