Close-up of flintlock action
You can clearly see the flint held in the jaws of the hammer. The way this action works is that the flint strikes sparks off the frizzen (the long upright, slightly curved piece), which fall onto the priming powder in the cup and hence via a flash hole to the main charge. When not required for immediate use the frizzen is swung down over the cup and helps, "to keep your powder dry".
