When I was a young teen, I really got into reading the few Star Wars novels that existed at that time. After I exhausted the then current run of books (there were only about 5 or 6 of them), I decided to read the novelizations of the original trilogy.
I no longer own those novels, so I can't look up the reference, but I recall that during the beginning of A New Hope, when Luke and Obi-Wan rode into Mos Eisley on Luke's land speeder, George Lucas mentioned something of there being a "dog barking".
This always struck me as odd because this was a reference to an animal from Earth in a universe where, clearly, most creatures were completely unique.
After noticing the reference to a dog, I then noticed on the my next re-watchviewing of ESB that there was a snake on Dagobah.
This has made me curious for years. What other Earth-based creatures have made their way into the "official" Star Wars universe and where do they appear?