What did Will mean by his comment that Granny was the only one who had ever be interesting about who died and what has the word levitation got to do with this?

Will meant that the stories Granny told about people who died were interesting because she was a good story teller. He mentions that all grown-ups in Sassy Tree enjoyed talking about who died of what, but Granny was the only one who made the stories interesting to listen to.

Levitation comes into this because one of the stories Granny told had to do with the death of her Aunt Beppy; Beppy was said to have had the power of levitation; she died of typhoid on her wedding day.