Well, not exactly a scare but my first computer had a very unconventional case with an EXTREMELY small fan on the bottom of the case and no side exhaust or even side panel fan, for that matter.
When I was trying to install my first bit of RAM all those years ago, I put my case up atop my soft, fluffy-padded chair so I could see everything, because trying to see a screen AND a PC under your desk would require X-Ray vision. I didn't have X-Ray vision at the time so smoke ensued when the padding clogged the fan hole so no air could get in and the result was a new something or another.
I didn't get the blame because it was the parental authorities idea. Now I know better and my cases ALWAYS have front and side fans. LOTS of fans.
And now that my X-Ray Vision has developed, I can now work in the dark, underwater and upside down on my computers. Three cheers for being pelted by Gamma Rays. The only bad thing is I now have a slight green tint in my skin... meh. It's prolly just the magic marker the kids next door up on me while I was sleeping.