User blog comment:DancePowderer/Who's Afraid of the Big Bad Caribou?/@comment-147.144.63.146-20101102195739/@comment-1595565-20101103014204

It's not water, Sanji's head couldn't be seen and water could never become that viscous. I thought it might have been glue. While not naturally occuring, it would explain how the cannon ball went in but not out of him. It's something sticky, of that much I'm certain.