It could be an urban legend, but this one’s not. When you set out to travel by airplane this holiday season, to visit family and friends, or go on a vacation or business trip bearing gifts, beware the power of cheese. Amy Von Walter is a spokeswoman for homeland security in this region and explains some food items can trip a security scanner. In some cases, the density of cheese, peanut butter and chocolate will cause a false alarm on the machines that scan checked bags. They sense a certain density and Von Walter says you don’t want to trigger that automatic system. If you’ve got any of those items, take them in a carry-on bag, not a checked suitcase because if it sets off the alarm they’ll have to take the bag out, open and search it. There’s another warning for lovers of literature. In checked bags, don’t stack books on top of each other because that also will trigger the density sensor in scanning machines and cause a false alarm they must check out. Homeland Security screeners who have to search a bag will cut a lock if it’s necessary, though they will reseal the luggage. Von Walter says if you want to lock your bag, you might use plastic zip-ties, so if it’s chosen for a search the tie can be cut and opened, and they won’t have to cut off a lock.