Lost World, The (Jurassic Park) - Splash on Camera
In the scene where what-his-name (please tell me what his name is) is walking through the river with all the tiny dinos attacking him,watch in slow motion and you will see a drop of water hit the camera lense.
(I have to give credit to my friend Noah for this one)
This type of thing happens in a lot of movies, especially in a lot of Spielberg's ones. Try Saving Private Ryan or The Original Jurassic Park, for instance. Often times, as I believe happened here, directors (and Spielberg loves to do this) leave this in as a way of bringing the action even further out to the audience.
My fellow movie-going friend and I have seen this happen a lot, from water in a big splash to blood gushing from a wound in a horror movie. I've seen it so many times I've regarded it as commonplace in most instances and don't really consider it a slip-up per se, but that's just my opinion.
Spielberg has said, in many cases, that that is kind of his "thing". He loves leaving splashes on the lens because it makes you feel like you are there. As for "Saving Private Ryan", that was COMPLETELY intentional, as per the director himself!! NOT A SLIP-UP AT ALL!!!!!
I agree with everyone else who said that it was Speilberg trying to get the audience into it. It's in so many movies that i consider it some what of a special effect. It could be a blooper, but I doubt it. Good observations, though!!!!!!!!