For some reason, the saliva-covered hat, which Mr. Harvey uses to gag Susie, is what convinces Abigail that Susie is dead. Why is this more convincing to Abigail than the elbow? Well, because she recognizes it. She made it. It's a psychological thing.

Some of the worst words a parent can hear.

This intimate knowledge of the details of her daughter makes us feel Abigail's love for Susie. It also pleases Susie to no end, because she's in the phase of her ghosthood where being remembered and talking about is very important.