The verbal irony in the passage is: Doesn't sound too bad. I'll try and stay awake.
Verbal Irony is a type of speech in which the understanding of the author's words is actually the opposite of what is said.
In the sentence by the Grandson, we find the usage of verbal irony because the content of the book is actually scary but he said that it does not sound too bad. So, in this context, verbal irony is used.
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