I never even thought of locking a bag right before the x-ray or putting stuff away...

What can happen inside a machine where a human can't fit and where you see your bag going in and then you see it again coming out on the other side?

I usually put my laptop, cellphone and wallet on a tray, the bag behind it, I'll put them in, walk through the screening and then on the other side I put cellphone and wallet back into my pocket and laptop inside the bag. It takes me 20 second from the beginning to the end...