Quite the surprise, this. I don't think I've ever actually seen an Elaterid beetle that wasn't already in the 'click' position - head, antennae, and legs tucked in, lying still and waiting for a moment to click those two spikes on it's thorax against its 'shoulders', with enough elastic force thus released to launch them high into the air away from predators. Or back over onto their front, since they also do it when they're stuck on their backs.
As you might guess from the large eyes, usually active at night, which is another reason I haven't seen them unfurled before.