Owners with outdoor cats may not be able to observe the symptoms associated with litter box use and should watch for unusual behavioural changes. If the cat is indeed blocked with a urethral plug, as time passes, the bladder fills up with urine and causes painful bladder distension. The cat becomes increasingly distressed, and may howl or cry out in pain. The male cat may constantly lick at his penis and the penis may be protruded. The cat may seek seclusion, stop eating and drinking, begin to vomit, and become lethargic and eventually comatose as toxins accumulate in the bloodstream.