Strange Cactus

About a month ago this "spike" began to grow out of this cactus. It grew very,very rapidly, maybe six inches each hour. You could almost watch it grow in real time. Click on the image to make it bigger.

After it reached full height it developed "flowers" Small at first but then in a few days they got larger

In the last couple of days they are changing color and getting larger. They are turning yellow

You can also see, by comparing them to the other cactus that this one is dying.