In Messiah, you can display both sides of an object instead of just only the positive normal side.

To do so, I select "render" tab, then "surface" tab, then clic on "defaut" under object name. And then I can see under the surface tab, another surface tab, with "double sided" option.

But instead, I will flip hidden objects, in messiah. It take not so much time and it will render more quickly.

"Display normals" would be a good feature to add to Moi.

Thanks everybody for taking time to help me.