The demon is described as a "parasite". Parasites, however, are characterized by feeding off of, but not killing their victims. As this demon kills its victims, it is therefore a predator not a parasite.
When Buffy is gouging out the demon's eyes, her thumbs are clearly just being over its eyes and no actual gouging is being done.
When Willow wakes up on her first morning back in Sunnydale, CA and tries to speak to Giles in the UK, she is told he is in a meeting all day. California is 8 hours behind the UK, so assuming that Willow rings at 8am, that would make it about 4pm in England. Giles would be free anytime soon, so Willow could have left a message and stayed home safe.
In the scene where Buffy and Xander are talking to Spike at the same time as Willow, we see a part of the Spikes dialog repeated. The first time he says the line "Someone isn't here," to Willow, he simply says the line. When he says it again to Buffy and Xander, he says the line followed by a clap and chuckle.