I was given this plant by a co-worker, who didn't know what it was. I have been told variously that it was a dog tail cactus, a monkey's tail cactus and a rat tail cactus. But its flowers don't look like the flowers on any of those cacti. They look more like oxalis flowers. The buds appear, folded up, on thin stems that shoot straight up. As the flower unfolds, the stems bend and droop. The flowers last for weeks. Also, the spines on this plant are not sharp -- they are soft, more like hairs.
It looks like a rat-tail cactus to me, I got a good laugh about the oxalis "flowers".
You may have trouble getting the oxalis out . . . they are bulbs and will come back if you don't get the bulb out.
It's a nice oxalis so if you manage to remove it replant the bulbs in another pot.
Thanks! You know, it never occurred to me that there were two plants in that pot. Now I know why the "flowers" looked so familiar. I'm not going to remove the Oxalis, though. I get a lot of comments on my cactus with the funky flowers!