diff --git a/src/docs/user/userguide/differential.diviner b/src/docs/user/userguide/differential.diviner
--- a/src/docs/user/userguide/differential.diviner
+++ b/src/docs/user/userguide/differential.diviner
@@ -66,6 +66,7 @@
   - diving into the details of inline comments in
     @{article:Differential User Guide: Inline Comments}; or
   - reading the FAQ at @{article:Differential User Guide: FAQ}; or
+  - talk like a cow at @{article:Differential User Guide: Cowsay}; or
   - learning about test plans in
     @{article:Differential User Guide: Test Plans}; or
   - learning more about Herald in @{article:Herald User Guide}.
diff --git a/src/docs/user/userguide/differential_cowsay.diviner b/src/docs/user/userguide/differential_cowsay.diviner
new file mode 100644
--- /dev/null
+++ b/src/docs/user/userguide/differential_cowsay.diviner
@@ -0,0 +1,59 @@
+@title Differential User Guide: Cowsay
+@group userguide
+
+Overview
+--------
+
+Cowsay is a Perl program by Tony Monroe which has been ported over to
+Phabricator/Phorge to allow your differential comments to be voiced by
+a cow.
+
+Basic Usage
+-----------
+
+A basic example of using cowsay would be to add a comment
+  cowsay{{{Great work!}}}
+which generates:
+```
+ _____________
+< Great work! >
+ -------------
+        \   ^__^
+         \  (oo)\_______
+            (__)\       )\/\
+                ||----w |
+                ||     ||
+```
+
+Other Cowsay Templates
+----------------------
+Other templates are available in externals/cowsay/cows/ eg:
+  cowsay(cow='tux'){{{Great work!}}}
+generates
+```
+ _____________
+< Great work! >
+ -------------
+   \
+    \
+        .--.
+       |o_o |
+       |:_/ |
+      //   \ \
+     (|     | )
+    /'\_   _/`\
+    \___)=(___/
+```
+
+Other Parameters
+----------------
+* think (set to 1 for thinking bubbles)
+* eyes (default 'oo')
+* tongue (default '  ', try 'P')
+
+Next Steps
+==========
+Continue by:
+* @{article:Differential User Guide}
+* @{article:Differential User Guide: Inline Comments}
+* @{article:Differential User Guide: FAQ}