James,
Thank you for your Borromean rings node.

I particularly liked the dip.
So: Union two intersecting circles, and fillet the two resulting "corners".

It might be nice to have a node to do this to a line, or a curve.
Then apply it to the limaBean curve Z value...

- Brian

curveDip.js, a Transformation?
center of dip.
length of dip along line.
depth of dip at 90 degrees.
appropriate circle radii, (or arc radii), and fillet radii?
Make one dip. (Union makes two dips, but cleans up the leftovers.)
(Union of two arcs leaves the tails as leftovers.)
Use the results to apply to a portion of the Bean for the z value...

Apply proceedure to a curve?