This tendency to drop words means that declarative sentences sometimes merge into exclamations. Where in English we might say "My hand hurts!" (which might be rendered literally as "Watashi no te ga itai desu ne!"), in practice one would be much more likely to say simply, "Hurts!" ("Itai!"). In English, we have separate exclamations for such occasions ("Ow!", "Ouch!", etc.); in Japanese, the exclamation is just a shortened version of the declarative sentence.
This crops up in other contexts, too. If something is delicious we might say "This is delicious!" (declaractive) or "Yummy!" (exclamation); in Japanese, "Oishii!" serves both purposes. If something is cute, we might say "That's cute!" (declarative) or perhaps "Awww!" (exclamation). In Japanese, both are "Kawaii!"
When I was in Japan in last month, a cute dog came into the room where I was with my Japanese friend, and she not only exclaimed "Kawaii!", she said it at frequent intervals over a period of a couple of minutes, as if keeping up a kind of running commentary on her own feelings. (To be fair, the dog continued to be cute for the whole of that time.)