(True bombardier beetles are fascinating for a number of reasons: evolutionary, ecological, chemical, taxonomic, you name it. To begin with, they’re ground beetles. Ground beetles are in the Adephaga, which are the irritable country cousins of the beetle family: the name means “eats a lot” (more or less), but really sets the Adephaga apart is their sheer biological creativity at squirting things out the other end. I’ll probably write more about them at some point, but regrettably, I won’t be able to use a photo of a local bombardier beetle as an excuse. As far as I know, there are none in Washington state.)
At any rate, this is a darkling beetle, probably Eleodes obscurus. They’re also called “stink beetles”, which suggests that while the Polyphaga may not match the Adephaga in their dedication to secreting things, they do get by.
This is definitely a case where I let my aesthetic sense get in the way of an easy ID: this is not the best angle for telling Eleodes apart (the head is hard to see), but it’s not often that you see an insect show such dedication to simple communication with passing mammals. Most insects are only interested in communicating with each other, and I thought the effort deserved some respect.
Come to think of it, the only other example that comes easily to mind is the warning buzz from a bumblebee who’s thinking of going into nest defense mode. The content of the message is strikingly similar, too.