The Mesh Repair Control window opens.
Red arrows appear, pointing to problems with the mesh, if any. The prompt line describes what type of problem the arrows represent.

The control window displays mesh information (statistics) and whether or not the mesh satisfies the criteria (passes the tests) defined above. These criteria are examined, and related problems are fixed, one at a time.

Once the process terminates, the mesh boundaries are drawn in red.

See Mesh > Mesh Repair
for a detailed description of the Mesh Repair Control window.
Mesh Repair handles Mobius strips by displaying a set of triangles which, when deleted, should remove the embedded mobius strip(s).