Pencils are totally useless to rewind cassete tapes the fast way. That is, hold the pencil up and swing the tape around like a ratchet. They're way too thin and don't catch the teeth, forcing you to hold the pencil at an awakward angle.
Bic pens fited perfectly between the teeth, almost as if it was designed that way.
@JoeKerr Pencils were in no way worthless, but you had to put them in at an angle and twirl the pencil, or similarly try to have them at an angle while spinning the tape. So more like Casper actually said, they were a bit more difficult to use = pens were better. XD