--- a/Doc/library/unittest.mock.rst	2017-01-11 09:41:19.105862456 +0100
+++ b/Doc/library/unittest.mock.rst	2017-01-11 09:56:28.372688309 +0100
@@ -1846,6 +1846,18 @@
     >>> sentinel.some_object
     sentinel.some_object
 
+Sentinels are designed to be equal only when identical. Any operation which
+results in copying, such as pickling, will create a different object.
+
+    >>> orig = sentinel.some_object
+    >>> copied = copy(orig)
+    >>> orig
+    sentinel.some_object
+    >>> copied
+    sentinel.some_object
+    >>> orig == copied
+    False
+
 
 DEFAULT
 ~~~~~~~