Asbjørn had been having some 'quiet time' most of the day, up in the forested areas along the north border of the city, but decided to swing by Howl Barrow in the evening to pick up something he'd left at work. That's when he sees a few posters, and stops. Although he is definitely not a cruorvore, it creates a deep-seated sense of unease.

He probably doesn't even realise he's letting off a few inhuman chuffing noises while he stands there reading, but considering how he's spent his day, it's unsurprising that that part of him is close to the surface.