The beheading by terrorists of a third hostage over the weekend with threats to kill other captives prompted psychological experts to warn the public that viewing the ghastly videos can cause trauma. The slaying of British aid worker David Cawthorne Haines - which Prime Minister David Cameron called \u201cevil\u201d - was seen in a video released Sept. 13 by the extremist group Islamic State. Haines, 44, was taken hostage 18 months ago in Syria. The videotaped murder is said to be similar to two others in which American photojournalists James Foley and Steve Sotliff were slain by a black-hooded and masked terrorist speaking English with a British-sounding accent. As in the earlier videos (Sotloff\u2019s was released Sept. 2 and Foley\u2019s just days earlier, in late August), the executioner threatened to kill another hostage, the New York Times reported. The Islamic State extremist group, also known as ISIS, on Saturday released the video, titled \u201cA Message to Allies of America.\u201d Post-traumatic stress disorder specialists say that even limited viewing of such menacing and heinous violence could be psychologically harmful. \u201cIf I was going to give a tip, I would say my advice for both adults and (obviously) children, is, do not watch the beheading,\u201d said Roxane Cohen Silver, professor of psychology and social behavior at the University of California, Irvine. Dr. Silver was part of a team that studied the effects of viewing repeated news footage of the Boston Marathon bombing, the 9\/11 terrorist attack and the Iraq War; their research study of adults, announced in December, found more psychological trauma befell viewers of repeated news reports than actual victims or witnesses of the bombing event. \u201cI\u2019ve told that to many of the reporters who've called me over the years,\u201d Dr. Silver told Promises Behavioral Health. \u201cThey\u2019ve asked whether they should watch these videos; this has been going on since the beheading of Daniel Pearl,\u201d the Wall Street Journal reporter kidnapped in Pakistan and later slain on tape in early 2002 by terrorists. \u201cI see no psychological reason and certainly no benefit to watching these videos. And it feeds into the terrorists\u2019 hands.\u201d Experts Shun Footage The potential damage from watching such grisly images prompted Silver and her colleagues to make a decision for themselves about the videos. \u201cOur research was not focused on a single image. But I\u2019m certain that for some people it is traumatic to watch the video even a single time. I had the same conversation with my research team when the beheading (video of journalist James Foley) came to light. We agreed we wouldn\u2019t watch it. It also plays into the terrorists' goal of spreading fear and anxiety.\u201d Some journalists have felt compelled to watch the disturbing videos in order to accurately report on them, but very few others would have need. One exception: those whose job it is to protect the rest of us from seeing such material. They review and remove offensive and abhorrent content from websites. A former Google worker told Buzzfeed.com that it was his job to hunt down and screen the most horrific images on the search browser \u2013 from child porn to beheading footage. After less than a year, the experience, he told BuzzFeed.com writer Reyhan Harmanci, forced him into psychotherapy. \u201cI dealt with all the products that Google owned. If anyone were to use them for child porn, I\u2019d have to look at it. So maybe like 15,000 images a day,\u201d the unnamed employee told Harmanci. \u201cI had no one to talk to. I couldn\u2019t bring it home to my girlfriend because I didn\u2019t want to burden her with this . For seven, eight, nine months, I was looking at this kind of stuff and thinking I was fine, but it was putting me in a really dark place. Google got someone from a federal agency to talk to me, and that\u2019s when it occurred to me that I needed therapy. She showed me photos of seemingly innocuous activities (kind of like a modified Rorschach test) and asked me for my first visceral reaction.\u201d He told her it was demented. But \u201cit was just a father and a child.\u201d Risk for Long-Term Damage In the UC Irvine research last year, which examined trauma caused by repeated exposure to news coverage of a large-scale devastation such as the terrorist attack at the Boston Marathon, the team found recurring symptoms long after the exposure. Research subjects reported more intense symptoms than did witnesses to the attack, the study team found. If you or younger family members have seen any of the terrorists\u2019 videos, or a traumatic event, keep an eye out for sleep disturbances, and returning or intrusive thoughts about the disturbing images or experience. While PTSD is most often associated with war veterans because their symptoms first led to it becoming an official diagnosis in 1980, an estimated 60 percent of all men and 50 percent of all women will experience a traumatic event in their lifetime. Eight percent of those men and 20 percent of those women will be diagnosed with PTSD symptoms. Symptoms include: \tReliving the trauma through intrusive thoughts or nightmares \tEmotional numbness \tMemory loss \tIntense feelings of anger, guilt, worry, hopelessness \tAvoidance of reminders of the trauma In the case of children\u2019s exposure to the disturbing images, and to trauma in general, Dr. Christine Courtois, a nationally-recognized trauma expert, said to watch for signs such as sleep difficulties or excessive worrying. \u201cFollowing a traumatic event, keep an eye out for an unwillingness to go to school or to be in public places, or nightmares,\u201d said Courtois. \u201cIf the child\u2019s behavior becomes markedly different - for example, they appear to be depressed or very worried, they eat much more or less than usual, they have difficulty concentrating - they need additional reassurance and support. \u201cSome children may need treatment to reduce their fears. Talk to a school counselor or therapist to learn more about short-term, focused treatments available for children, such as Eye Movement Desensitization and Reprocessing (EMDR) and specific protocols associated with phobias. Parents can also find useful information online provided by the National Child Traumatic Stress Network and International Society for Traumatic Stress Studies.\u201d If you suspect your kids have caught sight of the videotaped beheadings, or if you are concerned that a peer might show them the videos or that they will find them online, talk about it as a family. \u201cDealing with an event such as this doesn\u2019t mean pretending that it isn\u2019t happening,\u201d said Dr. David Sack, CEO of Promises Behavioral Health, which provides treatment for mental health conditions including trauma. \u201cYour child is going to know something is going on, and trying to hide it will only increase their anxiety. Your role is to be in charge of the message and tailor it to the age and the personality of the child.\u201d Sack reminded parents that they have other, more subtle ways to ease trauma. \u201cWatch your tone of voice and your body language. Your child will be looking to you to determine if he or she should be fearful. Above all, assure them that you are there for them and that they are safe. \u201cTell your child what you know about the situation, tailoring the details to their age. A teenager, of course, can deal with, and should be getting, much more information than a preschooler. Encourage questions and answer as honestly as possible, but don\u2019t feel you have to get into every frightening detail. The younger the child, the broader the brush.\u201d Click here for more about trauma.