This is a good example of a baby squirrel with pneumonia. This can happen due to exposure but more importantly due to improper feeding technique. Squirrels can aspirate formula if held in the wrong position or if they are allowed to drink too quickly. The formula enters their lungs and the moisture allows infection to set in. So if you're trying to determine whether your baby has pneumonia, watch this video. It is crucial to put a squirrel in this condition on antibiotics immediately.
To reassure anyone that has a pneumonia baby, there IS hope! A course of Baytril fixed Fudge right up and he went on to become...
...a champion eater.
...and a champion cuddler (he's the pudgy one)