It’s hard to know what to expect when going through airport security. Sometimes you’re able to waltz right through without a second glance. Other times, you find yourself being interrogated for a suspicious used Kleenex in your purse ("Ma’am, I’m afraid you’re going to have to check these boogers"). Either way, it’s important to know what’s allowed and not allowed on a plane. For example, a hairbrush? OK. A stun gun disguised as a pink phone? Maybe not.