I think its because he fainted or so because the police might think hes dead
This is only an idea, but an advantage could be that you don't have to wait for it to dry and disadvantages could be that you don't get as vivid colours?
Mr. Birkway was not upset with Phoebe because he read her suspicions out to the class in her private journal, he then explained to Phoebe what happened regarding Mrs. Cadaver, Mr.Cadaver, Mrs. Partridge, and himself.
That is "Fountain" by Marcel Duchamp
plaster because that the only thing that they had to work with.