Hexes and X's

I couldn't tell if some of the silly things in the book were supposed to be jokes or just mistakes.
I'm pretty sure the grammar errors were not jokes. For a comedy, if it was a comedy, there was a lot of dead people. In one case, somebody is assumed to be dead and nobody checked to see if they were.
Here are two examples of silly things that took me out of the book. I'll mark them as spoilers but I don't know that they are. In the sense of giving away the solution, or revealing a surprise, I don't think they are spoilers but they do tell you about events that happened in the book.
Spoiler one, about civil engineering.
I'm not a civil engineer but I did study some of it.Somebody (not sure who, I really couldn't tell who the bad guys were) built a set of traps, one of which involved traveling through sewer. This meant that this person tapped into the nearby towns sewer system, extended it for a mile or so to the mystery house, ran it uphill inside the building ( I think, I had trouble understanding the geometry), ran it through the building and then back to town. This is ridiculous.
Spoiler two, this involves fire department equipment
One of the traps (called hexes in the book to support the cute title) involved snakes. Later in the book, the local fire department is called in to retrieve several bodies and they have to go through the snake room. Somebody asks how they will get past the snakes, they pull out a crate of mongooses from the fire truck! I laughed heartily at this. My wife is a trustee of the local fire district and assured me that mongooses are not standard fire equipment.
On the whole. I didn't like this book and don't recommend it.