Weird symbol under the character after [Empty] was equipped

I was climbing the road to the shrine of Azura, south of Winterhold. At the top of the road, there was a frost troll. As the road is very steep, I decided to Fus Ro Dah his ass and watch him faceroll to his death downhill, which is what happened. But then something unexpected happened. As soon as my Fus Ro Dah landed on the frost troll, it was written " was equipped" at the top left corner of my screen. I guess I must have equipped Nothing… but what is Nothing? I don't know. at the exact same time I looked down only to see i was walking on some weird blueish transparent icon thing that is indefinitely emitting a frostbite-like spell effect (it's stuck under my legs and it doesn't go away, whatever i try to do). I can't properly describe what the weird blueish transparent icon thing looks like because it is self-aware and seems to be shape shifting everytime I look at it from a different angle.

My question is pretty simple: What the hell happened?

I don't know if that frost troll is always there, but let me quickly enumerate the steps to reproduce the event.

1. Have Unrelenting Force level 3
2. Approach the said frost troll (at the top of the road leading to the shrine of azura)
3. Fus Ro Dah his ass and watch him faceroll to his death downhill.
4. " was equipped"
5. Forever ride a mysterious blueish transparent icon thing
6. ???
7. Profit

Images:

Other images:

• image 1: location
• image 2: troll
• image 3: fus ro dah (" was equipped" at the top left corner of this image)