RDH,
Here's a pic that'll help Rocket's explanation.
When the ejector trip rod inside the reciever is pushed out, it'll trip that sear, release the hammer, and the hammer
whacks the ejector. The hammers in the picture are "fired" and will be cocked when the gun is closed.


And OT to my friends here, I did round off the fore end despite all the comments regarding it's
quadrilateral appearance *sniff*