Smurf Rescue has an interesting Easter Egg: a naked Smurfette! Smurfette really does lose her clothes in this game. If the player crouches when Smurf finally finds Smurfette, her dress will magically disappear. Getting her dress off is quite tricky, really, so the guaranteed way of getting Smurfette naked is to enter and then exit the final level (the room with the skull). Watch carefully as you exit - what a naughty Smurfette!
Of course, this is a programming error, not intentional. According to the people at Intellivision (one of Coleco's competitors in the 1980s), the nude Smurfette appears due to sprite limitations (when a white part of the Smurf's body is directly in line with Smurfette's white dress, one of the two white areas must go - in this case, Smurfette's dress is removed). So the rumors are true - due to a programming mistake, improper game testing, and some luck, you too can see a nude Smurfette!
What happens to Smurfette's clothing once you undress her? It floats around the screen, of course! After you enter and exit the final screen, simply wait around - Smurfette's dress will float all over the screen, forever.