The lizard's back is the softest part? Since when has that ever been the case with a shelled creature, at least aim for the underbelly or it's neck. Honestly anywhere would've been better than it's back.
Also the author really set up that metal lizard huh? Mentioned it and 2 seconds later it showed up. Really threw me off the trail with that whole, "well, I guess it really doesn't matter since I won't come across them," line, totally believed that. I suppose next chapter I should expect he'll meet a dragon as well, or maybe some new monster that was briefly mentioned will show up out of the blue.