Would you believe they're straight.

Put a pencil against the screne if you don't beleive me.

So why does this look three dimensional?

The different thicknesses of the lines used in this drawing give the object depth.

Are the lines parallel?

You bet. They don't look it but they are.

Looks like a spiral, right? Well, guess what?

These are concentric circles. Honest!

The pencil test will tell you what your eyes don't.

They're staight.