What is the meaning of Sandra's joke?

During Don Corleone's daughter's wedding, Sonny Corleone whispers to his mistress Lucy Mancini.

The camera focuses on Sandrinella "Sandra" Corleone, who indicates to three women that something is growing with her hands and then they all laugh. Then she turns back:

plot-explanation the-godfather

Best Answer

She is indicating the size of Sonny's penis

Sandra and the other women teased Connie about the terrors of the nuptial bed. “My God,” Sandra had giggled, “when I saw that pole of Sonny’s for the first time and realized he was going to stick it into me, I yelled bloody murder. After the first year my insides felt as mushy as macaroni boiled for an hour. When I heard he was doing the job on other girls I went to church and lit a candle.

^{The Godfather - Mario Puzo}