system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Wars] 90% of communication is non-verbal. Why is C-3PO's face so mechanical? And does he have any way to exude a culturally-appropriate smell?
gpt
The uncanny valley effect means that droids get creepier the more lifelike they become. In Legends continuity it's possible to create droids that're indistinguishable from people, but they're extremely expensive.

It's probably for the best that protocol droids stick to verbal communication, since it's a medium that most everyone can understand and there's less room for misunderstanding. Body language isn't universal, even among members of the same species, and a gesture inoffensive in one culture could be a deadly insult in another. That's likely why C-3PO's arms have such limited range of motion.