Apparatus described herein includes a tube, shaped to define a tube lumen and including a distal portion that has a plurality of articulated sections. The apparatus further includes a ribbon that passes longitudinally through the tube lumen and is connected to a distalmost one of the articulated sections, and a control handle disposed at a proximal end of the tube, the control handle being configured to flex the distal portion of the tube by pulling the ribbon. Other embodiments are also described.