Now a snake, especially a wary old python like Kaa, very seldom shows that he is angry, but Baloo and Bagheera could see the big swallowing-muscles on either side of Kaa's throat ripple and bulge. (3.73)
Kaa is plotting his revenge against the Bandar-log, and it's going to be fierce. They called him names, but it looks like he's going to swallow them whole. Words may never hurt you, but they may cause a giant snake to come out of the jungle and eat you.