Physical Characteristics

• Healthy kittens will be firm, warm and plump. Unhealthy ones have poor muscle tone. Healthy kittens nurse and sleep most of the time at this point.
  
  

Behavior

• Healthy kittens are quiet and sleep a great deal. They do not cry or make a lot of noise. Unhealthy kittens are very active initially and cry often. When healthy kittens do make noise, it is in the form of squeaking to communicate hunger or hissing if frightened. This is also when kittens begin to purr.
  
  

Weight Gain

• Healthy kittens should be consistently growing and gaining weight. The average weight for a newborn kitten is 3.5 ounces, or 100 grams. By the end of their first week of life, their weight should double.
  
  

Other Changes

• You should notice that healthy kittens begin to respond to sound at one week old. This is because kittens are born blind, deaf and with a limited sense of smell. While their eyes should still be closed, their hearing should begin to improve at this age, though not drastically.