diff --git a/docs/MainModule.rst b/docs/MainModule.rst
index cc9ee9a..1f13d60 100644
--- a/docs/MainModule.rst
+++ b/docs/MainModule.rst
@@ -67,11 +67,19 @@ not be able to find any collisions with those shapes anymore.
 
 
 
-Bookkeeping
------------
+Shapes
+------
 
 See also the :doc:`Shapes` sub-module.
 
+.. note::
+
+  HC will only keep `weak references
+  <https://www.lua.org/manual/5.1/manual.html#2.10.2>`_ to the shapes you add
+  to the world. This means that if you don't store the shapes elsewhere, the
+  garbage collector will eventually come around and remove these shapes.See
+  also `this issue <https://github.com/vrld/HC/issues/44>`_ on github.
+
 
 .. function:: HC.rectangle(x, y, w, h)