SDO/AIA 171 Å images of the loop before and during the oscillation. The dashed red line (left panel) shows the elliptical fit to the loop axis. Slits (solid blue lines) are taken perpendicular to this axis. The middle panel shows the loop after the lower leg (red arrow) has been displaced by the CME. The right panel shows the apparent plasma outflow (purple arrow) associated with the CME which obscures the view of the lower leg for most of the oscillation.