diff --git a/docs/writing/gotchas.rst b/docs/writing/gotchas.rst
index f8e2e23..fcf1439 100644
--- a/docs/writing/gotchas.rst
+++ b/docs/writing/gotchas.rst
@@ -76,6 +76,7 @@ signal that no argument was provided (:py:data:`None` is often a good choice).
         to.append(element)
         return to
 
+Do not forget, you are passing a *list* object as the second argument.
 
 When the Gotcha Isn't a Gotcha
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~