Isn't it suspicious how spiral Zeus can be so strong and yet act like a retarded idiot obsessed with poop. You know who else acted like a retarded idiot but was much more? Tobi did before he pretended to be Madara and then became Obito. My guess is spiral zetsu's stupid personality is all an act and just like Tobi he is much more. Who spiral zetsu is and whether Madara really knows who it is is unknown but I believe it may have a big role to play in upcoming chapters.