They normally flower after Daffodils and before Tulips and come in two colours - one is white, but the other is a sort of checkerboard design of purple with cream. I like the latter best.
The plants are allegedly difficult to establish, but once established are reliable performers and lend themselves to naturalisation in a part of the garden that doesn't get dug - for instance a patch of "Wild Flower Garden" or meadow. They do best in cold, damp conditions, although they do enjoy sunshine.
As the buds swell they turn a darker colour and fill-out in size. This is the stage at which they most closely resemble a snake's head.
Later on, when fully open, the flowers look a bit like Tulips.
Here's a close-up of the snake's tongue:
I have some of them growing in a border, and some in this pot (hedging my bets again).
One thing I have noticed about this flower is that it is exceptionally hard to take a good photo of it. The "checkerboard" design is blurred at the edges and tends to make the photo look out of focus. I must have taken at least a hundred shots to produce the ones in this post!