I was exploring the jungle when I found an enderman shivering without attacking me, probably because I was in Creative mode. So I tried spawning some of them with the spawner eggs and noticed that the ones who were spawned on any block were normal, the ones I spawned in the air, after taking fall damage began to shiver, open the mouth... As they do when angry against the player or another mob. I'm not sure if it happened also before, but I've never seen an angry enderman wandering in the jungle! I hope I've been useful!