So I'm going down the road in the 2002 pt cruiser and as I start to slow down at a light on the way to school I hear a rather loud crack, much like the sound a hot dashboard will make when it expands in the sun.

No big deal right? I look around and don't notice anything out of place...

on the way home I notice that the outer edge of the passenger side mirror glass is bowed out a little bit giving me an odd mirror effect. Upon further inspection it is indeed bowed, and even slightly cracked on that edge line basically from top to bottom.

Keep in mind that this is on the back side of the mirror, not the front. Frontal inspection revealed absolutely nothing out of the ordinary such as bird feathers or even a scratch.

So now my question to you all is can someone explain what happened?