"It's actually not as odd as you may think, friend.

Kaa is an Indian rock Python, and on average for the majority of pythons, roughly 90% of their body is made of muscle. Now, the average, healthy, ten year old boy with an average height weighs something around 70 or so pounds. Plus, the fact that Mowgli grew up being fed such pure and lean meat by wolves.

Now, the average Indian Rock Python (in the wild) is said to be something around 15 feet, and weigh around 115 pounds. In the original story, it was said that Kaa was something like 30 feet long, so from that information and some math, I've concluded that Kaa would weigh about 230 pounds, and 90% of that is pure muscle. 207 pounds of pure muscle, carrying around a 70-something pound boy.

See, it's really not so complicated.

And yes, I have done my research. Hope that my explanation was satisfying." -Youtube Indian Rock Python Expert

My favorite crime: Expectation
My favorite punishment: Disappointment