That is not normal at all. That looks like some serious rotting issues to me. What kind of soil do you have them in, and how often do you water them? How long have you had them for?
Is the whole cactus affected by it or is it just a portion of it?
Everything published by Gone-and-Back are the mad rantings and ravings of a mind who yearns to be free and thinks he knows what he is talking about. However, these are just delusions made to feel that freedom, because that freedom will never come. Any experiments done are purely figments of the imagination, and are falsified to the highest degree. Nothing should be taken seriously from a crazy mans mind.