This scene is cut from the Empire Strikes Back.  In the original script,
several Wampas (the Abominal Snowman-ish creature that beat-up Luke) were
captured by the Rebels.  When the Imperials attacked, C-3PO pulled off a
warning sign and several Imperials Snowtroopers walked in unknowingly and
were mauled.

For more information, go to http://www.evan.org