Toward the bottom of page 46, Stanley puts the stationery back in the box after he realized Zero was behind him. Then in the paragraph after Squid and Armpit call for Caveman of page 47, he puts it away again after he says, "Uh, sure."
NOT A SLIP-UP!!!
It says "He [Zero] just stared at the letter with a serious, almost angry look on his face.
Stanley slipped it back into the stationery box."
This is obviously refering to th LETTER not the stationery which he later puts away. I suggest this slip-up is corrected. Pronto!