Overall Appearance
Sometimes there isn't any one thing, but the whole picture that looks off to you. The cat may be sitting hunched up. There may be an expression of pain on its face. Its coat may have lost its luster and pliability.

All Changes
In general, any abrupt or severe change is cause for immediate concern. For example, a cat that suddenly becomes unable to use its hind legs needs to see its vet right away.

Once you decide to seek veterinary care, you might have to choose between seeing an unknown emergency veterinarian after hours or waiting until your cats regular veterinarian is back on duty.

Here are some signs that always warrant immediate care.

• Any trouble with breathing, seizures, protracted vomiting, paralysis, hemorrhage, or straining to urinate may represent life-threatening emergencies, says Julie Levy, DVM, assistant professor at the University of Florida, College of Veterinary Medicine.
  
  
• More subtle signs include jaundice (yellow tint to the gums, eyes, and skin), pale gums indicating anemia or shock, [and] abnormally high or low body temperature, Levy says. Delaying treatment for these disorders, if even for a few hours, can make the difference between recovery and death.

Trust Your Instincts
There is much to be said for an attentive owners instincts. Sometimes you can't identify what is wrong, but an alarm bell goes off inside you. This is also a good time to see a vet, who is trained to put the medical puzzle together.

I once took a cat to the vet and apologized for coming in because my only worry was that he wasn't racing me to the fridge, says Margo Mann of Victoria, B.C., Canada. He was, however, eating. After blood tests and radiographs, he was diagnosed with pyothorax a serious infection in the chest cavity. He was completely cured and lived to be 15."

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