“Q: What is the difference between the dreams of men and those of beasts?
A: The dream state is common not only to all men, but also to all animals, of course, from the highest mammalia to the smallest birds, and even insects. Every being endowed with a physical brain, or organs approximating thereto, must dream.
Every animal, large or small, has, more or less, physical senses; and though these senses are dulled during sleep, memory will still, so to say, act mechanically, reproducing past sensations. That dogs and horses and cattle dream we all know, and so also do canaries, but such dreams are, I think, merely physiological.
Like the last embers of a dying fire, with its spasmodic flare and occasional flames, so acts the brain in falling asleep. Dreams are not, as Dryden says, “interludes which fancy makes”, for such can only refer to physiological dreams provoked by indigestion, or some idea or event which has impressed itself upon the active brain during waking hours.”
H. P. Blavatsky
The Mark Of God: Understanding Your "I AM Presence" 