I LITERALLY was thinking about this exact thing earlier today. How humans have a preternatural sense of knowing something is watching them or even hunting them. Humans are animals, and while our other senses are dulled in comparison to other animals... we still have them.
And applying that to GRACE, a pretty chill human, who is in the presence of another fellow predator but an alien one, it just leads to such intetesting possible dynamics between them!
Do Eridians have a similar preternatural "6th sense"? Do Eridians get adrenaline Fight/Flight/Fawn responses? Because I imagine they do get adrenaline spikes (the moment where Grace is getting crushed by his chair and the centrifuge force leads to think Rocky lasted as long as he did was because he had his own form of adrenaline propelling him past his body's natural limitations) But the preternatural sense is the big question here. ALL animals on Earth have it. It comes with living in a fairly hostile enviornment, including Rocky's look-a-like, spiders, who are primarily ambush based predators.
And humans seem to REALLY be attuned to that sort of predatory tactic. I can imagine Rocky trying to startle Grace, and getting really freaked out by him spinning around to clocking him immediately, but then because Rocky is an 'alien'-- would that trigger Grace's own survival instincts? Would Rocky then get his own preternatural sense triggered as suddenly, every cell in his body is telling him to RUN from Grace, as the startled human feels something is hunting him and is now in an aggressive and defensive stance. (A lot of hostile energy is being channeled at Rocky suddenly. Would Rocky be able to sense that, as Grace seems to be able to?) Intelligent predator meets intelligent predator, and instincts are going haywire for a few seconds.
And Rocky, staring down Grace that is towering over him, with a very flexible and agile form that emmits a blinding cacophony of noise (heart rate picking up, breathing shallowing) and can't help but be grateful that his body tempature is scalding hot to Grace.
And then Grace snaps out of it, and he starts grumping that Rocky should stop that, he looks like a giant fudging spider, and it's freaky as heck when he sneaks up on him like that. Wait, how did he know he was there again? What do you mean, 'you don't really know,' you just 'felt it'??!