Before the body was sent to the crematorium, shilling and Crump filled the casket with animal bones, meat, and a mannequin.
Object of the preposition: genius. The subject of the sentence is called a noun clause. It is a clause because it has its own subject and verb. It is also a dependent clause which cannot stand on its own because of the word that (a relative pronoun) at the beginning of the clause. A noun clause functions as a regular noun in a sentence.
A prepositional phrase consists of a preposition plus a noun or pronoun (the object of the preposition). Object of the preposition is just a fancy name for the noun or pronoun that that follows the preposition. In our apple example above, apple is the object of all of the prepositions. It is the first noun listed after each preposition.