Originally Posted by
atbPy
It is for Secondary Security Screening Selection. In my case, I had to change travel plans from domestic to a Canada trip a few days before my departure. On my way back I got this great experience. They will go through absolutely everything in your carry-on and you get the pat down.
And it truly is
absolutely everything. That isn’t an exaggeration. I’d plan to put anything non-essential and non-valuable in your checked bag if you have one and keep your carry-on as light as practical.