Scared

Why is that a child that typically walks like an elephant can still sneak up on you and scare you so bad you jump and almost hit the ceiling? saac was working on school so I went down stairs to switch laundry. All a sudden Isaac is standing in front of me. "Mommy I am done "he proclaims. I jumped and he could not keep from laughing as he hugged me and says "Mommy I have never scared you before."