No one would have ever guessed by looking at him that Optimus was sick. At night we would put him in our kitchen (his purr was so loud it woke us up) and he would climb up the counter, get on top of the cabinets, jump out of the kitchen transom (small window above doors in old houses) onto the steps, climb upstairs and get into bed with me. He did this multiple times one evening before we realized what was going on. All this from a cat that was supposedly sick!
Optimus was a great patient, and great medical care was able to give him a happy, though short, life. After a year we lost Optimus, but adopting him was one of the best decisions we ever made.