My mare used to lose her brain while being tacked up and would be exceptionally spooky and bronc-y while under saddle. Turns out that, while her saddle fit in the traditional sense, there was something about it that SHE didn’t like. I tried a different saddle on her and it was like night and day. She retained her brain through the entire session.
RE: animals faking injuries. Now, I’m not a vet or anything like that, so I can’t claim scientific knowledge on the subject, but I wonder if it’s possible for horses to learn a behavior to get out of work. For example, a horse that has been pinched by a cinch being tightened too quickly will continue to snake their heads and nip until they re-learn that tacking up doesn’t have to hurt. I don’t know if that can extend to faking a limp, though. That being said, I have a rescue dog that nearly lost her paw. She has contracted tendons and when she’s tired or has run around too much, she does limp. She also learned, as a street dog in Mexico, that she could play on sympathy. Big, brown puppy eyes and an exaggerated limp got her food. Now, I’m constantly amused by how she “plays” my friends. She’ll walk fine and soundly all day until she hears a bag of chips or something open, and then suddenly, her paw is the most painful thing ever. She limps and she cries and she carries on until one of two things happen – either she gets a treat or she gets told to stop begging. At that point, the limp magically disappears as she walks out of the area. It’s rather amusing. I imagine horses are capable of the same actions, but I don’t know if it would be considered “faking” an injury.