If Eusine's smile falters when he realizes there's a massive language barrier between then, it doesn't show for more than a microsecond. No problem! He can work with this. His new alien friend looks willing to communicate, which is an excellent start; he may or may not have noticed Nihlus' gesture of irritation (the mandible thing reminds him of that one time he found a crab cryptid. Good times, good times... until it tried to eat him, at least) but Eusine would never let something as petty as mild annoyance prevent him from butting into people's business.

"This," he tells Nihlus slowly and loudly, arms outstretched towards the landscape as if trying to embrace it all, "is EARTH! EARTH." he repeats, drawing a circle in the air with a finger. The planet you're on. Earth.

He is communicating with an unknown alien species. As the common man would say, this is so cool.