In The Time of Dinosaurs

I saw myself playing with the little plastic figurine - a plastic toy model of the animal whose belly I was in. A booklet had come with the figurine.
I'd memorized all the facts in that booklet.
<They were wrong,> I thought as my mind shut down. <It's bigger than they said.>

[...]

I drew back my massive paw. The paw of a grizzly bear. A paw that could destroy a man with a single, backhanded swipe. I drew that paw back and I extended my wicked, hooked claws, and I thrust that paw straight out. I twisted and pushed. The twist ripped and the power of the thrust dug my paw deep into the creature's in-sides.
"HREEEEE-UH!"
I heard its scream. It reverberated through the flesh that pressed all around me.
I thrust and twisted.
"HREEEEE-UH!"
Another scream. A spasm that wracked the body so powerfully it almost knocked me out.
But I was not so easily crushed now. I was no longer human. I had finished morphing the grizzly bear. And not even this sea monster could digest a grizzly bear.
With my last ounce of strength, I thrust and twisted.
SHWOOOOOSH!
Air!
Air poured in. I gasped at it. Air!
I had done it. I had ripped a hole out of the gizzard and penetrated the creature's lungs.
<Tobias! Breathe! There's air!>
I went back to work, ripping now with both huge paws. Digging downward to avoid the ribs.
Suddenly water gushed in. Salt water. Cold and wonderful. I kicked and clawed the opening till it was bigger.
Then I tumbled out. I hit bottom. I looked up, dazed and disoriented.
The creature had beached itself. I was in no more than five or six feet of water. I stood up, my huge bear head broke the surface, and I reared up on my hind legs.

[...]

<Yeah. And let's see, if I remember my old dinosaur books, those
long-necked things in the water were Elasmosauruses and the thing that
you just chewed a hole through was probably a Kronosaurus.>