Brief GIM Explanation

GIM, or Get Items Manipulation, is a glitch that allows one to collect an item in an unintended way.

GIM is performed through first initiating a glitch called Walking While Talking (WWT).  WWT is done by collecting an item for the first time with an altered camera.  The altered camera results in the game not pausing like it normally does when an item is first collected.  Then, taking damage during this non-paused collection allows Link to walk around with the item where it was when it was held above his head.  You may have heard this called Nuts on Links Face (NoLF).  With WWT activated one then assigns a value to a flag in the games memory by standing in front of a chest.  Depending upon the chest different values can be assigned.  WWT is then canceled by jumping in water.  This causes collection of the initial item as well as another item based on the value assigned via chest.  In 'No RBA/WW', light arrows are received.  In 'Any%', a blue potion.

GIM is a complex and confusing trick.  If you want to read more, here is a thread from when it was first found: http://forums.zeldaspeedruns.com/index.php?topic=1785.0

*Note* This is hard to explain.  If anyone reading this thinks I misspoke in explaining it, feel free to suggest a correction.