1.) If it sounds like a small pony; its Taz, my 20 poung (big, not fat) 11 year old neutered tom.
2.) If there's a bit of sound with an odd cadence; its Kasey, the 15 pound 8 to 10 year old rescue torti, she has an old left rear leg/hip injury that accounts for the odd cadence (She has been checked by the vet, she is on Dr. Maggie's Joint Formula amd is doing very well with the leg).
3.) If you don't hear anything; its Morgan, the 10 year old "tudeo" cat, she is the stealthy and graceful, perfectly proportioned mini-cougar