How is it possible to mistake a pack of Skittles for a loaded gun? Simple human psychology:

When people have a gun in their hand, they’re more likely to believe an object held by someone else is also a gun.
They’re also more likely to raise the gun to shoot.
Those are the key findings from a new study that will be published later this spring in the Journal of Experimental Psychology: Human Perception and Performance.
“The familiar saying goes that when you hold a hammer, everything looks like a nail,” write the two psychologists who authored the study, James Brockmole of the University of Notre Dame and Jessica Witt of Purdue University. “The apparent harmlessness of this expression fades when one considers what happens when a person holds a gun.”

Of course gun-wielding neighborhood watch vigilante George Zimmerman thought his hoodied victim was packing heat. Why wouldn't he?

All the more reason why I don't want to live in a society where a substantial number of citizens walk around armed—especially in a state like Florida where its "Stand Your Ground" law apparently makes it legally defensible to shoot me if you legitimately fear that my cell phone or my snack is a deadly weapon. I've had enough angry comments, emails, and phone calls over the years from paranoid righties insisting that I was bigger and more immediate threat than al-Qaeda, to suspect that at least some of them might actually believe it, and I'm not particularly thrilled about giving them the means and the legal cover to do something about it. Though, of course, it could be worse. I could be black.

But, you know, Second Amendment! and all that.