Definition: In this task, you need to generate an appropriate title for the given summary of some paragraph. The generated title must be short and should include the main topic of the given text. Your summary should be less than 20 words long.
Input: North Korea has hailed its sixth "perfect success" of a nuclear test. The seismic readings indicate it is bigger than any other it has conducted, but the apparent collapse of a tunnel at the nuclear test site could provide valuable information, nuclear defence analyst Catherine Dill writes.

North Korea nuclear test: 'Tunnel collapse' may provide clues