Thought

"You can still see the scars where those brains attacked me!"

- Ronald Weasley

Thought is the type of magic that allows the brain to think. In the Department of Mysteries of the MInistry of Magic, they study thought by keeping several human brains in a water tank. Occlumency is a type of magic that involves clearing your thoughts of all emotion. According to Poppy Pomfrey, thought can leave deeper scars than anything else.

Battle of the Department of Mysteries
"According to Madam Pomfrey, thoughts could leave deeper scarring than almost anything else, though since ahe had started applying copious amounts of Dr. Ubbly's Oblivious Unction, there seemed to be some improvement."

- Ronald Weasley's treatment after being attacked by thought

In the Battle of the Department of Mysteries, Dumbledore's Army and the Death Eaters fought in a room in the Department of Mysteries full of brains. A Confunded Ronald Weasley thought the brains were funny and summoned them. After the thoughts soared at him, they tried to suffucate him. When the battle ended, Madam Pomfrey said that it would leave a scar since nothing leves deeper scarring than thought.

""Hey, Harry, there are brains in here, ha, ha, ha, isn't that weird, Harry?...Honest, Harry, they're are brains - look - Accio Brains!" The scene seemed momentariarily frozen. Harry, Ginny, and Neville and each of the Death Eaters turned in spite of themselves to watch the top of the tank as a brain burst from the green liquid like a leaping fish...The moment they came in contact with his skin, the tentacles began wrapping themselves around Ron's arms like ropes..."Harry, it'll suffucate him!" screamed Ginny."

- Ron's attack by thought

Appearances

 * Harry Potter and the Order of the Phoenix
 * Harry Potter and the Half-Blood Prince