User blog comment:Kaido King of the Beasts/Chapter 893: Charlotte Snake and Snackman/@comment-24850639-20180208162511/@comment-29325824-20180208205138

I definetly think Smoothie's size changing is due to her own DF. Either she can grow due to absorbing fluids like a sponge, or she can shrink due to wringing most of her own size out (assuming she inherited her mother's size). Or a combination of both.