Book 1

We learn that, in the past, the Dursleys have given Harry an old pair of Uncle Vernon's socks for his birthday.
The very first time we meet Harry he is in his cupboard looking for socks.
Dumbledore tells Harry that in the Mirror of Erised he sees himself holding a pair of thick, woollen socks.

Book 2

At The Burrow, Mrs. Weasley is "fussing over the state of his socks."
And also at The Burrow: "Mrs. Weasley dashed about in a bad mood looking for spare socks"
When Dobby explains to Harry that, for a house elf, clothes means freedom, he says: "The family is careful not to pass Dobby even a sock, sir"
Harry tricks Lucius into giving Dobby Harry's sock.

Book 3

Harry uses Uncle Vernon's old socks to cover his Sneakoscope: "I never wear those socks if I can help it."
The Fat Lady is found hiding in a potrait of Argyllshire, a place famous for socks.

Book 4

At The Burrow, Mrs. Weasley washes Harry's socks.
On Christmas morning, Harry gives Uncle Vernon's "foul," "mustard-yellow," and "extra knobbly" socks to Dobby.
Ron gives Dobby an unwanted violet pair he got from his mum. Dobby is ecstatic. Ron (looking embarassed) says: "They're only socks..."
Dobby gives Harry a pair of socks; one red, with broomsticks, the other green with Snitches, that he knitted himself.
Harry resolves to buy Dobby "a pair of socks for every day of the year."
On the morning of the first task, Harry dressed so inattentively that it was a while before he realized he was trying to pull his hat onto his foot instead of his sock.
While Hermione is arguing with Hagrid about S.P.E.W, Hagrid is putting on socks.
Harry and Ron have fun in Hogsmeade picking out strange-looking socks for Dobby including "a pair patterned with flashing gold and silver stars and another that screamed loudly when they became too smelly."
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