Big fan of the idea that, from Erid's perspective, Grace is probably kinda scary, at first.
Like his language consists of noises that are simultaneously very simple compared to the overlapping eridian notes, and weird clicking/hard sounds that no one could even begin to try to imitate. To begin with, that's a weird combination.
And there's a popular headcanon going around that Grace can pronounce certain simple words in eridian without his piano thingy, and he would sound like a pebble learning to speak. Let's make it creepy and assume eridians also have a fear of the uncanny valley.
Grace getting better with time at imitating simple words, therefore accidentally making himself sound more and more like a pebble, sounding right enough, but not quite. That shit would be creepy as fuck.
Imagine an alien that can imitate the way the children of your species sound like. At first you'd freak out! Yeah he saved your planet but. It's like a fucking mimic. Then you'd see him trip over nothing and fall face first and you'd calm down.
This is probably a stretch but I don't care. I like to imagine eridians and humans have some very similar fears, and the uncanny valley potential is just too good to ignore.
