We are sure our dogs and cats dream. We watch them, asleep, go through the motions of life. Sometimes they add sound effects.
I never knew any of my lizards to dream, but I’ll bet my mice did. The jury’s still out on whether birds dream. If it turns out they don’t–is dreaming exclusively a mammal thing?
P.S.–I’ve just read about some French scientists who have concluded that, yes, lizards dream. But they were studying bearded lizards, which are about as close as you can come to being a mammal without being one.