This is an unopened flower of Scaphosepalum merinoi. You can also see the spikes with several more flower nodes just started. This blooms successively and the spikes continue to get longer endlessly, it seems.
Thanks, as always, Rosie. It did open and in fact, is already just starting to open in the picture. This is just a normal flower bud. The "horns" stick straight out when the flower is fully open.