I guess all those warnings about how Tylenol can damage your liver are true!
Ha Ha only serious. I can't find many decent references in a quick Google search, because all the links are "lolz teh armey is dropping Tylenol mice", but Acetaminophen is quite toxic to many animals, including house cats. It works as a poison by damaging the liver.
For a healthy human, the liver can metabolize a normal dose of Tylenol just fine... but if you combine alcohol, Tylenol, and a drawerful of other Acetaminophen-containing products (cough syrup with pain reliever, sleep aid with pain reliever, cocaine/speed/etc cut with pain reliever, etc), you've got trouble on your hands.
Also, there's the problem of would-be suicides who try to overdose on Tylenol-3, the prescription high-dose version with Codeine added. They generally don't die -- largely because there's a specific antidote that hospitals have to neutralize the Acetaminophen before it overwhelms the liver. Those who are too late for that intervention don't die either, not right away... they end up on the list for a donor liver, and get to spend their final weeks wishing that they'd either found a better way to get attention, or that they'd invested in a shotgun.