I was probably 17 and needed to do an oil change on my car. I got everything ready in the garage to get it done, turned on the radio, and got to it. I briefly thought about waiting until someone was home, just in case something happened, but I realized that I had done this many times before and nothing out of the ordinary would happen. I jacked the front of the car up, slipped the jack stands underneath the sides, and slid underneath. About half way through the job, as I was just about to replace the oil filter, I hear a strange groaning noise. I was laying on my back and it sounded like it was coming from behind me so I couldn't really locate the source. I also had a filter 3/4 full of oil and didn't feel like spilling it all over myself if I tried to spin and find out what was going on. As I'm screwing the oil filter back on, I hear the groaning sound again, except it's quickly followed by an ominous pop...pop...POP. The third pop was one side of the jack stand plate sheering off, sending the passenger side of the car crashing to the ground. It happened so fast I could barely react. I got lucky in four ways. The first was that when I turned my head to look for the popping sound, my arm ended up moving off of the filter and lined up with a more open spot of the engine bay. My fist still slammed against some engine component higher up, but my arm bones weren't shattered like they could've been. The second was that I was that I found the tip of my nose about an inch or so away from the bottom of the oil pan. If the suspension was any softer, my face would've been crushed. The third was that I had decided not to use the crawler because it was behind a bunch of plywood that I didn't want to move. If I had used it...well, see lucky thing #2. The third was that the jack stand kicked out, not in, when it failed. Had it come back in, it probably would've shot into the side of my head. I was able to slide sideways enough to get out from under the car. I grabbed another jack stand, hoping that the same thing wouldn't happen twice, and finished the job. Scared the shit out of me, though.