>>378823753
Oh yeah, a vector is just a line in 3 dimensions, so each face has a vector telling the direction of the normal. You can actually turn the vector all the way around so they point inwards, at which point you won't even be able to see the face unless it's using a two-sided shader. Flipped normals is another common problem you might see after merging meshes, but also easy to spot and fix once you know about it.