The Jungle Book
He is first seen trying to eat Mowgli by hypnotising him which fails after he gets hit in the mouth and then tries to hypnotise Bagheera which also fails. He is pushed out of the tree and (unsuccessfully) slithers away.
He tries to eat Mowgli again and sings to Mowgli a hypnotic song called Trust in Me but is interrupted by Shere Khan and is threatened by him. After Khan leaves Kaa says he gives him the shivers. He tries to threaten Mowgli but fails and slithers away again.
The Jungle Book (2016)
Kaa appears in the 2016 live-action film adaptation as the tertiary antagonist. Unlike in the previous adaptations, this incarnation of Kaa is a female, voiced by Scarlett Johansson. In this version, she is depicted as an Reticulated python, due to the fact that she is even more longer.
Kaa first appears when Mowgli stumbles upon her territory deep in the forest, after he is separated from Bagheera by the evil tiger named Shere Khan, where he discovers her shed snakeskin. After climbing into the trees and chasing animals that stole his food, Kaa begins to speak to him from above the trees before revealing herself to him.
Luring him in by promising to keep him safe, Kaa hypnotizes him and reveals that Mowgli came to live in the jungle because Shere Khan killed his father as they were traveling between villages, and that Bagheera later found Mowgli and brought him over to the wolves for protection. She also reveals to him the power of the "Red Flower" (fire) and its dangers in her vision. During her storytelling, she attempts to devour him, but a passing sloth bear named Baloo attacks Kaa and rescues Mowgli, freeing him in the process. Kaa isn't seen again for the rest of the film; it is unknown if Baloo killed her or she went away and never came back. During the end credits, however, she is heard singing her song, "Trust in Me".