Board Thread:Questions and Answers/@comment-28067574-20190904162421/@comment-32182236-20190910171416

It means that EITHER the light-blue human didn't die in the Ruins, OR the second human died before Toriel left. Otherwise, not every human who falls would leave, and then die.

And that flower showed up just before Toriel left. So it couldn't have been long after the flower was born.

So if the second option is true, the second human didn't fall that long after the first. If the first is true, the light-blue human didn't die in the Ruins, so something else is responsible for the items getting left in the Ruins. And since the door is one-way, the human lost them before going into the humans, and the Toy Knife ended up in the chest somehow.