The short version
Sanity is Animal Hospital's health meter: players start at 61-65% base (some classes start higher), and reaching 0% kills you. The wiki's documented values turn it into a manageable system — machine coffee restores 15% across three sips, a Chocolate Bar about 60% across three bites, tasing an anomaly pays +2 while tasing a patient costs 15, the Head Banger costs 20 for a coffee-less dismissal, cursed photo grabs cost 10, and a Bed Monster hold drains 10 then 5 every two seconds. Below 30%, even the wall posters change.