I got this cacti in the spring, I believe it to be a pin cushion cacti. Its bloomed three times since then, but just this last time a strange growth started to envelop one of the shriveling flowers. What is it?
It's probably fruit. The picture doesn't show much detail and its seems a little odd looking. Fruit doesn't normally displace tubercles, but who am I to tell a cactus how to behave.
If it is fruit it will slowly ripen and slide out of its current location. Don't tug on it, wait until it comes out with the slightest pressure.
On an unrelated note: Does the pot have a drain hole? If not you should repot into something that does. Cactus don't like sitting in swamps.