Another strange little cactus has decided to flower ... I've Googled this and it looks as if it's a Green Flowered Hedgehog Cactus.
First of all little round bumps appear, then under the bumps grow stalks. The bumps grow and expand and the cactus looks as if it has arms with clenched fists appearing. Then the fists open, and the pollen is visible. I suppose it has evolved in this way to avoid impaling its potential pollinators on some very nasty spikes ... isn't nature incredible!