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.
The object of the preposition is the noun that follows the preposition. It is also the stopping point for each prepositional phrase. For instance, we might say, 'to the store.' The word 'to' is the preposition and 'store' is the object of the preposition. Here's another example, 'in the light.' The word 'in' is the preposition and 'light' is the object of the preposition.