Revealing mistake: When Cindy hugs Tom (Charlie Sheen) and the razor blade gets stuck to his chest, the patch the blade is attached to under his shirt is visible. (00:05:45)
Revealing mistake: When Cindy pulls Mrs. Norris and places her hair in front of the fan, hair can be seen flying in the air before Norris' hair gets in the fan. (00:16:35)
Revealing mistake: When the little boy is killed at the boxing match in the flashback, you can tell the Don King-looking-guy is falling onto a dummy, and not the real boy. (01:00:50)
Revealing mistake: Halfway through the movie, with the crashed plane, the aircraft engine is actually running backwards.
Answer: Ads are often made months before the final editing of any movie. Therefore, it's not unsual for something to be in an ad but not in the final movie (or to happen differently, or a different shot, or different music, etc.).
Myridon