Final answer:
There is no 'Grout Monster' in 'Diary of a Wimpy Kid: Wrecking Ball,' so it is not possible to answer what proved its existence to Greg. If there is confusion, rereading the book may clarify the misunderstanding.
Step-by-step explanation:
The student has asked what proved to Greg that the Grout Monster was real in the book Diary of a Wimpy Kid: Wrecking Ball. This question seems to be based on a fictional scenario from the book series Diary of a Wimpy Kid, written by Jeff Kinney. However, within the book Diary of a Wimpy Kid: Wrecking Ball, there's no mention of a 'Grout Monster', which suggests that the student may be confused with a detail from the story. These books often involve imaginative elements and exaggerated situations to describe the experiences of the protagonist, Greg Heffley.
Without the correct context or a specific event from the book that includes the 'Grout Monster,' it isn't possible to provide an accurate answer. Instead, one might consider the themes of the series, which often revolve around the misunderstandings and comical misadventures that Greg experiences, whether at school, home, or in his social life. In general, these tales illustrate the humorous yet relatable trials and tribulations of middle school life.
In addressing questions about literature, it's important to reference the correct book and its content accurately. If a student is sure there's a reference to a 'Grout Monster' in Wrecking Ball, it would be advisable to revisit the book to locate the specific instance they are referring to for a precise answer.