This isn't really a true slipup, but it's something I noticed when watching E.T. in the movies. Towards the end of the movie when Elliot and his brother steal the van to take E.T. to the park, they drive over a curb and on to the grass. If you look closely, they actually turn sharply onto a small ramp painted the same color as the curb to get to the grass. This is easier to see in the movies but is visable on tape.