Cartoon smooth loops
This is a display setting. When set to off, the cartoon will follow a path that is splined between each alpha carbons. This sometimes yields representations that are pretty frizzy. Turning this setting on will make the cartoon follow a smoother (but less conservative) path so that the representation is easier on the eyes. Use with caution, since false conclusions can be drawn by solely examining a smoothed cartoon trace. It is always best (for non-representation purposes) to also have a line trace so that the backbone is precisely located.
set cartoon_smooth_loops, 1
set cartoon_smooth_loops, 0
I do not know precisely how the smoothed trace is generated, probably by some splining mode. Could someone more knowledgeable than me edit to be more precise ?