Creature sound design is probably one of the most creative, intense and interesting things a sound designer can do, whether for a game, film or TV series.
The trick remains on making the audience perceive this creature as being plausible and believable, and this has a lot to do with how it sounds: its vocalizations and sounds must 
fell natural, connect with the audience expectations and be understandable (when it fells sad, angry, happy, curious, etc).
A great example on this can be read on an article I wrote about No Man’s Sky Procedural Audio: the game sound designer, Paul Wier, had to develop an app that would generate natural and believable sounds based on multiple variables (the creature’s size, type, weight, environment, etc). It’s really interesting, and inspiring.
Anyway, this is not a new thing. Jurassic Park had a big challenge on creating the dinosaurs sounds (it was so successful that it created a pattern, and Jurassic World had to take it into account when they sound designed their dinosaurs).
About this, Beau Jimenez wrote a great article (Emotional Beings A Creature Sound Design Discussion) where he discuss the art of creating creature sounds, with some very good examples: the Jurassic Park Raptors, Toothless (from How to Train Your Dragon) and R2-D2 (no need to say where it is from, right…?!). Better: all of this with sound examples from each one.
Its a short but dense text, that can make you rethink (or start to think about) your method on creating sounds, not just for monsters and fictional animals, but for anything that the audience must relate to.
Just to give you a taste of it, I’ve selected some excerpts:
Now, regarding how we react to happy and sad vocalizations is a trickier topic. But on a parallel note: scientists don’t have an answer to why minor key music sounds sad and major key music sounds happy. But their theory suggests that the accumulation of media that we have digested since birth has made us react in a specific way towards music and sound. For instance, hearing a minor key song at a funeral or hearing a happy song in a major key at a wedding or celebration are examples of experiences in life that imprint on our aural expectations.
These vocalizations happen within minutes of each other in the movie, once Toothless sees Hiccup as a friend and not an enemy. This kind of design is superb because it breathes life into Toothless, the audience feels what Toothless is feeling, and lastly (and very importantly!): it feels like the same creature throughout, regardless of how many different animal species were layered and processed!
R2-D2 from Star Wars has a wide range of emotions as well. For the most part, he was written in the script along with his counterpart C-3PO, who translates for R2. I don’t know what the franchise would be like without 3P0’s translations, but I believe it wouldn’t be difficult for the audience to understand R2’s intentions and feelings. While there are organic qualities, the digital boops & beeps have rhythm, timing, and certain inflections that enlighten the audience to R2’s emotional state.
Sound designers have a unique duty in that we paint our canvas with materials that are sampled from our own beautiful planet. This idea has richness within it that other professions don’t. And utilizing a unique and unfamiliar animal sound layered with the precise emotional intent of our own voices can be a powerful toolset! (Don’t be embarrassed of sounding like a maniac as you yell into a microphone!)
Hope you enjoy it! 🙂
Mauricio Ruiz – www.mauricioruiz.me
P.S.: at first I thought that Jack Menhorn was the author of the article. He pointed out that Beau Jimenez wrote it instead. Sorry for the misunderstanding.
Audio & Music 