Final answer:
The first sentence is a complete sentence, but the second one is a fragment as it lacks a subject and verb. Sentence fragments can be corrected by attaching them to a complete sentence or rewriting them as complete sentences.
Step-by-step explanation:
The sentences in question are:
When Dustin Henderson left his Cheez-Its on the counter, his puppy ate them. Standing on her hind legs, shoving her snout into the box.
The first sentence is a complete sentence because it has a subject (Dustin Henderson's puppy) and a verb (ate), and expresses a complete thought. However, the second sentence is a sentence fragment. It lacks a subject performing a verb and doesn't express a complete thought. It simply gives additional information about how Dustin Henderson's puppy ate the Cheez-Its.
To correct the sentence fragment, you could combine it with the previous sentence or rewrite it to include a subject and verb. For example:
When Dustin Henderson left his Cheez-Its on the counter, his puppy, standing on her hind legs and shoving her snout into the box, ate them.
or
His puppy stood on her hind legs and shoved her snout into the box to eat the Cheez-Its.