The 9:30 Club welcomed The Books and openers The Black Heart Procession on Thursday night. First up, Black Heart Procession and a thoughtless series of randomly Googled images, bearing no connection to the music ho-humming from the speakers: a naked man lying in the snow, Cookie Monster, and vampires who are…fond of bondage. Up next, The Books and a visual element that was a perfect complement to the music at hand: thoughtfully chosen images that practically worked as an extra band member. Ebbing and flowing like the music it illuminated, the series demonstrated that The Books are hardly another experimental band playing with videos, strings, and effects pedals. They’re expressive, daring and somehow accessible — maybe that’s why their audience stood in rapt silence.