In the episode where Helga drops her little pink book on top of Gerald's Book. When they went out to find the person who wrote everything the left the book at home. Then Helga came and went into Arnoldss room to find the book and she found his sock and took it with her then Arnold came back so Helga hide in the closet and she still had his sock so the next morning when Arnold woke up he put on one sock then left for school.