This is a technique that lets you avoid waiting for the full collection animation in some cases.
There are three types of collection skip:
The game freezes time and ignores your button presses during the collection animation. However, there is a very small window (possibly a single frame) when you break an urn or flask during which you can open the menu. At this point, the item counts as collected, so saving and quitting will savewarp and preserve the item.
The other types of collection skip rely on the game advancing time while you are leaving the area. If you are off-center when going through an interior/exterior door, you are first centered, during which time your boomerang can continue flying toward its target. When timed right, much like Collection Freeze, you regain control due to the shorter animation ending. Similarly, when fast-travelling, the screen lingers as you turn to a cloud of nanites and speed away, allowing your boomerang to break an urn without interrupting the fast-travel animation. (The reason it doesn't work to throw the boomerang and then savequit, despite time resuming after the menu is closed, is that the save is from before the boomerang hits the urn, thus you can't collect it this way.)
Indra does not hit the urn for a couple of frames into her attack animation. Because this is very precise, you can practice without an urn. (Also you can practice in the main game mode, where you can exit to menu without saving.)
Drone can hit on the same frame as the attack.
TODO