App rejected- Apple wants me to add additional nat

Question

My recent iPad/iPhone Apps have been rejected. Apple's reason :

It would be appropriate to add additional native iOS functionality to the application in order to enhance the user’s experience. Specifically, features that enable the user to interact with the app rather than just consume information are recommended.

My App is like an album of cartoons of a specific theme (by a sports cartoonist). It has an initial thumbnail view, supports landscape/portrait modes, swipe for next/previous cartoons, Timed hiding/unhide of status bars/navigation bars etc.,. However Bookmarks,zoom , saving etc are not supported. InApp purchase of additional cartoons not supported. The App is written with iOS SDK 4.3 using Xcode 3.2

My specific question is : What is "additional native iOS functionality" ?.