Things that the cane may not detect, even when properly used in constant-contact cane technique, are:
Small objects or holes, which the cane may go around even when sliding on the floor in constant contact technique - see photos;
Poles and corners which the cane may go around (if the pole or corner is close enough to the cane hand, the shaft of the cane will contact it, otherwise no part of the cane will contact it and the person may bump into the pole) - see photos and videos;
Overhanging obstacles, such as tree branches, and signs or objects that protrude from a wall or pole - see photos.
These are illustrated in the video to the right and in the photos below.
CORRECTION in the video -- I mention that one way to make it more likely to find obstacles and poles or corners is to "shorten the arc" of the cane -- yikes!
I meant to say "shorten the STRIDE" as you walk forward, or shorten the distance between sweeps of the cane!
NOTES: The cane being used is 50 inches long (which reaches above the armpit and about 2 inches below the shoulder). It is moved in an arc 6 inches wider than the body -- click here to see a video explaining the dimensions.
For a written text of what is said in the video as well as description of the actions, click here.