My dog-tail cactus (Selenicereus testudo)does the same thing of some of the tails sticking up until they get to a certain length then they drop down. Most of you younger tails are the ones that are sticking up. That is why I thought it might be a cat tail.
The cactus that I have seen that have been said to be "The Old Man of the Andes" were more of a singular stem cactus that is very stiff and does not hang down.
