But of course, soap is only normal because we have always known it. On distant planets, other intelligent creatures do all sorts of things we would never dream of. If you'd never used it or heard about it, would you dream of soap?
Perhaps not, but you might dream of cleanliness. Do soap-like substances appear all over the universe? Life has been discovered in the frozen oceans of Europa. Soap would dissolve there. What would life be like in a liquid atmosphere?