So, admittedly, I'm terribly lazy.  I leave stuff in my car all the time.  And one of those was my water bottle.  It was empty.  I didn't need it.  Why not, right? 

This is why...

The bottle on the left is a brand new one (that I needed to get after "the bottle accident of 2012").  The bottle on the right is the one I left in my car overnight, maybe 12 hours.  These are identical bottles.  Bottles I would have previously thought as rather sturdy. 

If this can happen to a simple, I'll still even say, sturdy bottle, imagine what could happen to your pets or kids!?  Never, ever leave ANYTHING in a car, even with the windows cracked or open!