# Why subdivided faces with smooth shading acting weird?

I have this model, and when I add the subdivision-modifier:

it seems to be okay, for me (I guess those bumps are there, because of the triangle faces instead of quads):

I think this is something really obvious -- but I just can't figure out the reason..

The most likely reason for this is your object normals are facing the different directions at these edges. To fix, go into Edit mode, select the mesh and recalculate normals with CtrlN, Or you could manually select faces and flip the normals.

You can often confirm or investigate most most odd looking artifacts on your models by enabling a normal display type under Mesh Display in the Toolshelf (N). On a clean model, depending on the use case, both the vertex and face normals should point outwards.

• Thanks, I figured out, a few minutes before you, although I started to flip the normals manually -- thanks for the global recalculate tip:) – Peter Varo Dec 28 '13 at 23:29
• Enabling backface culling is also a good way to quickly spot flipped normals. – ideasman42 Dec 29 '13 at 2:02