One of the more amusing examples was Ripley(sp?) from the 3rd Alien movie does a long distance one handed backward basketball shot that they were going to use CGI on. The funny thing is watching the movie you see very honest surprised emotions which seem almost to believable.

However, the actress actually made the shot during the take which is why all the actors have a much more believable WTF expression than normal. The only thing out of place is the actress expression where she must have been trying really hard not to blow the take.

Edit: https://www.youtube.com/watch?v=rOrTfA8QZyI 4:35

Anyway, my point was if she missed then nobody would have thought it odd. They were not going to try again until it happened, but once it did happen they wanted to use that 'good luck'. It’s sort of the best take effect, walk around and take 1,000 pictures and the chances are something unusual happens in that shot. The odds of that specific unusual thing happening are not high, but the odds of some unusual thing happening is.