When Apple rolled out its latest handsets, the iPhone 6s and 6s Plus, the company took great pains to highlight a snazzy feature called "3D Touch". With the help of a pressure sensitive screen, users can more efficiently access the phone's various menus and options. Turns out, Instagram is working on a very similar feature for its Android app, no pressure sensitive screen required.
Honestly, it's really just a glorified long-press menu. When looking at another user's image grid, you can press and hold on a thumbnail to pull up a near full-size preview image. Conversely, drag your finger to the edge of the screen to shrink it back down. Hold and swipe down towards the Share and Like buttons to activate them -- all without lifting the finger. This feature is currently in beta but is expected to migrate to the official app within a few update cycles.