In the Haunted House, you are supposed to hide (click text or hit spacebar) when the vampire gets close. Though when she catches you get a couple of bonus CGs so worth getting caught at least once. Keep the light on Astrid until the bar fills up. You need to do this 3 times and after this the Vampire will show up when you return to your room. NOTE - You do not actually get Vampire Spit here I think it is a visual bug, you get it on the 4th time of completing the Haunted House after doing anal with Astrid.