In the 2008 movie *The Dark Knight*, Lucius Fox and Bruce Wayne have the following conversation in Hong Kong, prior to Batman capturing Lau (*err, spoiler alert? :-)*): > *Bruce Wayne*: What's this? > *Lucius Fox*: I had R&D work it up. Sends out a high-frequency pulse... records the response time for mapping an environment. > *Bruce*: Sonar. Just like a... > *Lucius (interrupting with a smile)*: Submarine, Mr. Wayne. Like a submarine. <br> My question is: **Why did Lucius interrupt Bruce and interject with "submarine"?** Was it just a subtle bit of humour to subvert the audience's expectations that they were going to compare it to bats using sonar to navigate? Or am I missing some other context (I'm not a reader of the comic books)? For reference, one can [watch the relevant clip here, starting at 5:10][1] (it's not my clip). [1]: https://www.youtube.com/watch?v=3h8mm5YZb88&feature=youtu.be&t=310