I'm a beginner in Computer Graphics and today, I encountered the concept of "manifold". And according to the brief interpretation in Wolfram MathWorld: (http://mathworld.wolfram.com/Manifold.html), if we can "walk around" at any point on an object, then it is a manifold.
I know this question may sound stupid, but according to that interpretation, is everything around us in the real world is manifold? Because even at the tip of a knife, I can "shrink" myself to "walk around" there. Or please give me some non-manifold examples(I mean, in the real world).
Thanks a lot.