Jurassic Park - Disappearing Ground

After the T-rex eats the goat and discovers the fence is turned off, she is walking on solid ground. T-rex walks through the fence between the cars. Later, T-rex returns to get Tim and pushes the overturned car, forcing Dr. Grant and the girl over the wall. Suddenly the spot where T-rex was standing is a huge drop off. Who moved the earth? A minor mistake also occurs when the baby raptor is hatching. The egg turning machine is holding the hatching egg from Dr. Grant's view, but a second later from Mr. Hammond's view, the turner is gone.