Christmas cactus

I brought in both my Christmas cacti today from the cold frame in the garden. I haven't watered them, or even looked at them since the end of August, and they are both covered in buds. This is the only flower so far, but I suspect now they are indoors all the buds will come out at once.

Both these plants flower about 4 times a year. Usually this is because I have neglected them each time they have finished flowering, and then suddenly remembered and given them loads of water. They then burst into flower again.