What it is
Cats are nimble, but curiosity sometimes takes them too far: through an open window or onto a balcony, onto a hot hob, into a fight with another animal or out into the street. After a fall from a height they can hurt their chest, jaw and legs, even if they land on their feet.
Some injuries are plain to see straight away, while others show only after a while. A bite wound is barely visible in the fur, but an abscess can form under the skin, and organs damaged by a blow may give no sign at first.
An injured cat does not always show that it hurts: it may simply hide under the bed, move less or stop eating. That is why after any fall or accident it is better to have a vet examine your cat, even if it seems fine.
Signs you may notice
A cat limps, bleeds, has a swelling somewhere, licks one spot, hides, refuses food, or breathes faster or harder. A few days after a bite, a painful lump can appear.
When to see a vet
After a fall from a height, a road accident or a burn, with a bleeding wound, or if your cat struggles to breathe, a vet is needed immediately. After other mishaps, have your cat seen by a vet the same day, even if it seems fine.
This is general information, not veterinary advice. For your own cat's health, tests and treatment, see a vet.