Thanks for the replies, but hmm. I drew the shape originally in the 'Draw' persona, using the pen tool, which leads me to believe it began life as curves. I have been able to edit the stroke thickness, which further leads me to conclude that it began life as a curve, not as bitmap art. Hitting cmd+rtn doesn't show any visual difference. Trying to add an anchor point afterward, using the node tool, still doesn't permit me to do anything but warp the selected curve segment. I can't add any anchor points. Screenshot attached in case seeing the UI's behavior will in any way help. (Note that the node tool doesn't appear in this screenshot, argh, but it's there, along with a little wavy line alongside the cursor that seems to suggest 'warp', since that's what happens when I click the selected segment.)