I had rescued 4 weeks old two squirrel babies on 26th July. We were feeding them puppy formula milk frequently first, and then gradually to 3 or 4 times a day. They were fond of grapes and pear. But they only ate 2 to 3 percent of one grape. And took only two small bites of it. They would have fruits only twice or thrice in a week. Otherwise they won't eat any in general. No nuts were fed.

Everything was fine till yesterday. Both were active and taking formula feed normally.

In morning they appeared fine, in noon at 2:30 pm, when I tried to pick "Charlie", it did not seem to be active as before. I doubted if it was sick. I offered him formula milk, it readily accepted and feeding seemed to be normal. I thought he might be sleepy and lazy. He had a habit of passing stool immediately after feeding. Today also he passed stool whilst I was holding him in my hands. But today stool was watery, with 2 to 3 yellow bits of nuggets suspended in liquid. 2 drops were passed then. After that I laid him in its house, thinking that he might sleep now.

After 2 hours I placed fruit slice in his house. Saw that his brother "Coco" was sitting active but Charlie was lying on his back, with all 4 legs spread in air. I thought it's his sleeping posture. Searched Google for squirrel sleeping positions, found one similar. So I thought that I will check again after half an hour and let me not disturb him.

After an hour I saw he was still lying in same position. I touched him and found out that "Charlie" was no more.

I am extremely shocked and surprised how so quickly Charlie passed away.

I examined him after that.
1. No injury mark.
2. Yellow semi liquid poop visible was under his tail.
3. Body was stiff as rigor mortis had set in. Belly was swollen, perhaps due to the same.
4. Mouth was closed, nasal opening had one (very small) frothy bubble.
5. Eyes were 95% closed and furry skin surrounding eyes was very wet.

Facts:
1. He was very active till yesterday. No signs of any illness.
2. Their house was extremely protective. No poisonous thing can be ruled out.
3. He took feed normally some minutes /hour before his death. He seemed lazy and showed less activity only at noon.

What could be the possible reason behind Charlie's death?

What might have gone wrong?

I want to know so that if I rescue a squirrel in future I should keep a check.