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 noun phrase or pronoun that follows the preposition is called the subject of the preposition. For example, behind the couch is a prepositional phrase where behind is the preposition and the noun phrase the couch acts as the subject of the preposition.