Final answer:
Dashes are the correct punctuation for non-restrictive clauses containing surprising information, as they add emphasis to the content. Parentheses, on the other hand, downplay the content they enclose.
Step-by-step explanation:
The correct punctuation for non-restrictive clauses that contain surprising information is dashes. Unlike commas or parentheses, dashes are used to emphasize the content within them. For example, if a sentence reads 'The kitten, which we found in the alley, has a rare breed,' using dashes instead could add emphasis: 'The kitten—which we found in the alley—has a rare breed.'
Both dashes and parentheses can enclose nonessential information, but when the goal is to emphasize the surprising information in a non-restrictive clause, dashes are preferred. Dashes also help to clarify meaning when an appositive phrase contains commas, as they prevent confusion with the list of items.