It makes for a fairly impressive flame thrower if you use it on a cylinder vac!
When I was younger, my dad asked me to clean and vacuum his old Ford Cortina while he was at work as, having just bought a new car, he wanted to sell it. When I tried to use our old 1960's Electrolux cylinder vacuum cleaner, which he kept in his workshop, I found the motor was seized up with debris from the reusable cloth dustbag as it had come open at the bottom, so I stripped the motor down cleaned and freed it up, fixed the electrics and checked it still worked. Then emptied and sorted out the bag.
Then as I was putting the bag back in, I noticed the inside of the metal case had surface rust, and had the not so bright idea to give it a spray with WD40 and wipe it down with a cloth. Now the suction chamber of a 1960s electrolux vacuum cleaner is not very wide, so I'd sat the motor end of the vacuum on the floor and inverted the can of WD40 and gave what I thought was a light spray, wiped it down and put the cloth bag in and reattached the front and hose.
Sat the vacuum on the back seat of the car and turned it on, and a massive jet of flame blasted out the rear through the open car door, narrowly missing my right leg and making a nice scorch mark on the creosoted fence several feet away. Luckily I didn't set the car alight!