Why did Aunt Sponge and Aunt Spiker scream and run for their lives in James and the Giant Peach?

After the peach has grown huge, the Centipede chews through its stem, which releases it from the tree on which it was growing. As the tree is on a steep slope, the peach is now free to roll down the slope.
Once the peach reaches the ramshackle house where James lives with his two aunts, it tilts the living room and sets the furniture sliding against the wall. The aunts were outside near the front gate, ready to sell tickets to the sightseers who came to ogle the giant peach. They are annoyed with James for not coming home. As they discuss how they might punish him for staying out, they hear an “awful noise.” At that moment, the peach crashes through the fence and rolls rapidly toward the two women. First they just stare, motionless, but then they scream, run, trip, and fall over each other.