"Very good, Neville. Two points to Gryffindor." Lupin continued, "Strictly speaking, a Boggart is a 'non-being.' Since it can turn into whatever anyone nearby fears, nobody knows what a Boggart looks like when it's alone, because it immediately takes the form of that person's greatest fear.
"Now, who can tell us what a 'non-being' is?"
Hermione, Harry, and the others lowered their hands. The rest still hadn't raised theirs, leaving only Will's arm in the air.
"Will, tell us."
"Non-beings, also known as non-human spiritous apparitions, are a category of magical creatures. They transcend life and death and have no counterparts in the Muggle world. Muggles can only perceive all currently known non-beings indirectly.
"Well-known non-beings include Boggarts, Dementors, and poltergeists.
"Most non-beings are connected to emotions, so most spells specifically used against them also involve emotions.
"Since non-beings cannot truly be destroyed, wizards have invented various spells to drive them away, reducing the conditions that give rise to them and keeping their numbers within certain limits."
Lupin applauded. "A perfect answer. I couldn't have answered better myself. Three points to Slytherin."
Lupin continued, "We have a considerable advantage over a Boggart. Has anyone noticed what it is?"
His gaze swept around the room, passing over Hermione, who was standing on tiptoe with her hand raised. Then he heard someone quietly say, "Because there are so many of us?"
"Exactly. When dealing with a Boggart, having more people actually leaves it at a loss." Lupin looked toward the speaker in the crowd. "Seamus Finnigan, right? One point to Gryffindor."
Seamus clenched his fist in excitement.
Hermione lowered her hand, looking a little disappointed.
"It won't know whether to turn into a frightening skeleton or a disgusting flesh-eating slug. I once saw a Boggart try to frighten two people at once