Lift piston broke through the chair and knocked on some poor soul's 'back door' always check the weight limit on chairs kids, especially if they have a compressed air piston under them, or you could get a piston enema as well.
I worked at a call center once and had a chair break in a similar way on me except it tipped me backwards and I ended up cracking my skull on a divider wall. Needless to say I didn't work there long after that, they fought paying for my medical bills trying to say I broke the chair on purpose. Even after everyone in the immediate vicinity of me said I had just sat down.
What