Board Thread:Questions and Answers/@comment-27713352-20161017031813/@comment-27321453-20161017040457

Grisha bit Frieda off her Titan's nape and I'm pretty sure he chewed her before swallowing her so she doesn't transform again inside his Titan belly (much like Eren and the bearded Titan).

And that was Rod who told Historia to bite through Eren's back and have some of his spinal fluid.

But let's face it, that part was only added to let readers know where the shifting abilities' located because what's the point of Rod telling Historia that when we all knew she'd be a mindless Titan and wouldn't be in control to specifically target Eren's back to begin with.

Not to mention he also said "You'll lose control once you're a Titan" and yet, still advised her to bite through his spine first? Lol.