Smooth

The Smooth command (Detail > Curves: Smooth) allows you to smooth two overlapping curves.

When two curves share the same end point, because of point merging or some other reason, the curve may not flow smoothly through that point. This can be particularly troubling when designing a complex spline cage. You could kill the curve (k), reselect the points and create a new curve, but there is an easier way.

To smooth curves sharing a common end point:

Select the two curves (Polygon Selection mode). 

Click Detail > Curves > Smooth. This smooths the joint as though the two curves were originally plotted as one continuous curve - even though they remain individual curves.