"So things that appear also stick around," Nel ventures. To her, it sounds like they get a copy of something that belongs to someone else and keep it in the same way the other person might. At least with memories she can write them down or draw immediately after to keep them fresh and detailed. That also means however any items that show up have to be kept hidden if they're odd enough to not belong with her other things.

"And you said doing something new makes the Echoes happen, right? So if I had never gone skydiving before, that might make me have one?" Extreme example, but also straight forward as something distinctly novel.