diff --git a/04-Return_Null.html b/04-Return_Null.html
index 37a720c..6f708d6 100644
--- a/04-Return_Null.html
+++ b/04-Return_Null.html
@@ -23,6 +23,14 @@
       </li>
       <li class="comment">
         the outside world (what happened, assumptions about what is)
+        <ul>
+          <li class="comment">
+            what happened: They came up with an alternative to asbestos.
+            Turns out that a precursor to the new material is even more
+            dangerous. A massive industrial accident happens.
+            At least, the material breaks down over time.
+          </li>
+        </ul>
       </li>
     </ul>
   </li>