The Police Manual was used by the Officer to note differences in animals.
History[]
When the Officer was about to take away Rudy and Slimer for having an illegal monkey. Rudy asked if the officer had something to distinguish monkey from a ghost. He pulled out the Police Manual. The manual noted that monkeys are brown, have a tail, and eat bananas. A ghost is noted in that book for being green, eating anything, and are extremely slimy.
Then Rudy pointed to the Organ Grinder that was seen with a monkey which was seen pick pocketing someone. The Organ Grinder tried to convince the officer he has a dog. However, the monkey actually takes the officers had book out and points out he is a monkey.