Why was Turtle startled when she looked in the coffin

Turtle had initially entered the Westing House on a dare. Turtle heard a whisper in the creepy house and found a corpse "tucked in a four-poster bed." A few days later, Turtle returns to the house to hear the reading of the will. She sees the open casket with the same dead man except she is startled to find the corpse was wearing an Uncle Sam costume.