The simple text is predictable, following this pattern:
He saw a/an [adjective] [Halloween object supported by the picture].
The last page breaks the pattern, allowing the teacher to determine if the student is attending to the text or reciting a memorized pattern.
High frequency words include he, saw, a/an, his, it, & was. Because the last page has was in the same position as saw on the previous pages, this book is useful for addressing saw/was confusions. Do this by drawing the student's attention to the first letter of was on that last page. Without confirming whether the child read the word correctly or not, ask her what sound that letter makes. Assuming she replies correctly, ask her if that is what she would expect to see at the beginning of was. By drawing her attention to this detail of the text, you are giving her the ability to self-check.