As a self employed mobile technician....
(WARNING: If you're eating you might want to, uh, not be!)
Not so long ago a customer of mine called me out saying his son's computer was overheating and shutting down. The son's father told me that he'd run the computer with no cover on for a few days as they'd fitted a new component and couldn't get the side panel to stay on fully. After a few days with the cover off they'd got it back on. This was under a dark desk.
Suddenly, it had started overheating. And, they'd not been able to find the family gerbil after it had gone walkabout, three days previous, after making a break for it from its improperly latched cage. I knew what was coming, and still can't get the image out of my head. The family gerbil, headless, decimated by the CPU fan (a high torque Corsair one), splatted all inside the case. It must have been snuggled in there as they put the cover back on, snuggled under the horizontal HDD cage so they didn't see it, where it had come out to investigate the big spinny, draughty thing later on. The guy had gone to make us all cups of tea. I didn't know how to break it to him, as his daughter loved the little furry guy.
I just walked into the kitchen and said, "I don't know how to break this to you, but I found the gerbil.....". He was smart enough to put two and two together. He told me not to bother cleaning the computer. "Chuck it in the bin, we'll buy a new one from you, and tell my son it is unrepairable."
Phew. I didn't fancy cleaning gerbil guts at all! Nicotine is nothing in comparison! The father kept the gerbil decimation a secret, and told the kids he'd escaped out the door or a window. I built them a new PC and had the old one shredded, I wasn't stripping it.....