These are the ripe spore capsules of cypress-leaved plait moss Hypnum cupressiforme - a moss with teeth.
Many mosses have teeth - peristome teeth - that surround the mouth of the capsule and regulate the dispersal of the spores. They're highly sensitive to changes in atmospheric humidity, so in dry air they curl back and allow the spores to be shaken out, just a few at a time, when the capsule vibrates on its stalk.
It's fascinating to watch the teeth uncurl and then curl under the microscope when you breath on them. They seem to be alive, although they're really formed from dead cell walls that react to changes in atmospheric moisture in the same way as the scales of a pine cone.