Den ekvivalenta scenen i boken är som följer, och lägger lite mer ljus på Lupins tänkande.
"I don't want to know how it fell into your possession. I am, however, astounded that you didn't hand it in. Particularly after what happened the last time a student left information about the castle lying around. And I can't let you have it back, Harry."
Harry had expected that, and was too keen for explanations to protest.
"Why did Snape think I'd got it from the manufacturers?"
"Because...," Lupin hesitated, "because these mapmakers would have wanted to lure you out of school. They'd think it extremely entertaining."
Lupins primära bekymmer är inte Sirius händer på kartan (Sirius har inget riktigt behov av det, han känner till alla Hogwarts och kan stjäl Harry i hundform, och Lupine borde veta detta ) , men att kartan kommer att dra Harry ut ur Hogwarts, där Harry skulle vara oskyddad. Värre, Sirius vet alla dessa vägar och brukar använda dem.
Medan Lupin inte (eller borde inte vara) orolig över att Sirius får kartan, är han inte heller glad att Harry inte ansåg det vara en möjlighet - som @Jenayah påpekar i kommentaren, hade Sirius tidigare fått tillgång till Gryffindor sovsal eftersom Neville lämnade en lista över lösenorden ut. Harry borde verkligen ha lärt sig av det här men behöll fritt med kartan oavsett trots att man visste att det listade flera dolda passager in / ut ur slottet.
Intressant nog verkar filmen kombinera två olika uppsättningar dialog här (Lupin och Snape, av alla osannolika par!). Scenen fortsätter enligt följande:
"Do you know them?" said Harry, impressed.
"We've met," he said shortly. He was looking at Harry more seriously than ever before.
"Don't expect me to cover up for you again, Harry. I cannot make you take Sirius Black seriously. But I would have thought that what you have heard when the dementors draw near you would have had more of an effect on you. Your parents gave their lives to keep you alive, Harry. A poor way to repay them, gambling their sacrifice for a bag of magic tricks."
Och tidigare i boken berättar Snape Harry
"Your father didn't set much store by rules either," Snape went on, pressing his advantage, his thin face full of malice.
Snapes dialog kommer helt och hållet från Lupine. Helt fint.