Grace wakes to Rocky’s tapping after oversleeping. To expand communication, Grace uses Popsicle-stick numerals to elicit Eridian words and records Rocky’s chord-frequencies. He writes a simple script that translates Rocky’s chords to English in real time, while learning Rocky’s words by ear. They add basic concepts like yes/no, build grammar, and note Rocky’s strong memory.

Grace presents a vial of Astrophage; Rocky confirms his star faces the same crisis. They exchange star names and define “sleep.” Rocky insists on observing Grace sleep, bringing a device to fix while watching. Grace relocates bedding to the tunnel and sleeps there nightly as their lessons continue.

Seeking a shared mass unit, Rocky provides a metal sphere and says “twenty-six,” which Grace misreads as a measurement. After an improvised zero-g balancing experiment with water, Grace realizes Rocky meant element 26—iron. Using calipers and iron’s density, Grace computes the sphere’s mass precisely and laughs at his detour.

Rocky finally needs sleep and asks Grace to observe him, saying it helps. When Grace suggests another Eridian, Rocky reveals he is alone; his original 23 crewmates died. Grace shares his own losses, and they touch the divider in empathy. Grace agrees to watch Rocky sleep, solidifying trust and companionship.