What makes a subject susceptible to Kaa’s Hypnosis?
Going off of evidence gained from the three encounters with Kaa across the original two animated movies, as well as his failure to hypnotize Shere Khan, I believe that three aspects of a subject’s personality influence their susceptibility to Kaa’s hypnosis: Fear, Individuality, and Desire.
I believe that fear plays a definite role in Kaa's hypnosis, as both Bagheera and Shanti were afraid of Kaa and dropped much quicker than Mowgli, who went slowly, and Shere Khan, who dropped not at all. But Bagheera, while afraid, was still able to eke out a "Please, Kaa". Shanti, however, fell almost instantly.
So while fear is a common denominator, I'm betting individuality and stubbornness, or lack thereof, plays a role too. Mowgli took the longest to fall in both his encounters because he wasn't afraid of Kaa, more annoyed and angry than anything. We know that Mowgli hates being told what to do, giving Kaa even less of a grasp. Nevertheless, I'm betting he took orders from his wolf family at some point. He knows how to obey, and chooses not to. Kaa is able to work around that, possibly by repeating the orders of an authority figure Mowgli has recognized (Bagheera telling him to go to sleep).
Shere Khan, who not only is NOT afraid of Kaa, takes orders from no one- he is infamous in the jungle for it. Therefore, he's not effected by Kaa at all.
Shanti, who not only was terrified when she met Kaa, is the poster child for conformity. She's the one constantly telling Mowgli not to go into the jungle, the one constantly trying to please her parents, etc. It's possible that Kaa's hypnosis places him as an authority figure to be pleased. Shanti looked at him in horror and saw someone bigger and stronger than her that she instinctively wanted to please. Only instead of her parents telling her to fetch water, it was a snake telling her to be eaten.
There is one more factor to discuss with Kaa, and that is desire. This is the section I have the least amount of evidence for, so it’s still largely theoretical. When Kaa hypnotized Bagheera, the panther was grinning even as he was resisting- Kaa was clearly doing something that felt good, and that weakened his resolve.
The other evidence comes from the second encounter with Mowgli. Mowgli clearly is still unafraid of Kaa, and still doesn’t see him as any sort of authority figure. Kaa has no “in” with Mowgli this encounter... until he hits upon Mowgli’s desire for friendship after his perceived betrayal.
This, coupled with his repeated assurances that Mowgli can “trust in him”, gave Kaa exactly what he needed to drop Mowgli.
What are YOUR thoughts on what makes someone susceptible to Kaa?