DAWN

If you watched Project Hail Mary but haven’t read the book yet, you might have wondered why Rocky first built a wall inside the tunnel between Hail Mary and the Blip-A with only one small window and only later replaced it with a fully transparent barrier. You could assume he was copying Hail Mary’s hatch, with its small round window, or playing it safe in case something dangerous came out of the human ship. But the book gives the real answer. Rocky doesn’t see. He understands the world through sound. So when he built the first divider, he wasn’t thinking "What if the alien needs to look through it?". He was thinking like an Eridian engineer! He filled the wall with different kinds of xenonite, hoping at least one of them would let the alien from the other ship communicate through sound and sense the other side by echolocation. And then one block just happened to be transparent xenonite. Rocky didn’t know that transparency mattered, but he accidentally gave Grace a window. Without that one lucky piece of material, the first contact between humans and Eridians would have been a lot more awkward.