What I Want to Know Is . . . - Fancy That

So, when you talk about events that take place in a book, you use present tense, right? As in, "Howl throws a magical hissy fit and there's green slime everywhere." But what is the protocol for describing your reaction to a book's event? Sometimes, it works okay to put your reaction in present tense: "It cracks me up when Howl throws that magical hissy fit." (Though is it me, or does that sound slightly weird? As if I'm saying I crack up every time it happens, when it only happens once in the book? Although, of course, I've read Howl's Moving Castle like twelve times, so I guess that "gets me every time" could be appropriate.)

In other situations, though, it comes out very strangely: "I'm startled when the guitar explodes." That makes it sound like I'm startled now. But if I'm reviewing or talking about a book, and I describe the book's events in the present tense, it doesn't seem right to suddenly shift to past tense for a sentence to avoid this: "They rush back into the castle. Then the guitar exploded, which startled me." It's maybe even worse to shift within a single sentence: "They rush back into the castle. Then the guitar explodes, which startled me."

I suppose a simple solution would be to put everything into past tense - "They rushed back into the castle. Then the guitar exploded, which startled me" - but I remember learning at some point that this was Not the Done Thing for describing events in books/movies/etc.

How do you handle this? Am I weird for wondering about it? I guess I write a lot of book reviews . . .