It comes out in Day9's video #252 - Secrets of Hotkeys, APM and Mouse Movement at the 41:00-41:10 minute mark. He grabs a small set up lings, and splits them up really fast without having to individually click each one. I dont think I read about this in my SC2 strategy guide, if I did I must have forgotten, but anyhow, Id really like to learn how to do that type of split, it is much needed in moments where I need vision.
he just selects all of his lings, sends them to one spot, then deselects one by clicking on the picture in the lower window while holding shift and sends the zerglings to the next spot. Since the one ling that was deselected doesnt get the new move command he moves to the first spot. Repeat for all lings.
When you have a group of units, if you want to select one of them you just click on it right ? now what if you want to de-select one of them, then you shift click on it. using this mechanic, when you have about 7 zergling. you can order them all to go somewhere and then deselect one and then order the rst to go somewhere else... delesect another one and again order the rest to go somewhere else, this way you leaving one zergling behind each time your deselecting and ordering the rest to move.
What he does is he selects all lings, clicks on a spot on the minimap, holds shift and left clicks away a ling from the control group, sends the rest to another spot on the minimap, shift left clicks away another, sends the rest to another spot and so on.
its called slicing according to a day9 vid i saw a long time ago.
Lets say you have 30 marines on hotkey 1
you hit 1, right click move to the right (any direction really) then you box a small chunk of the marines (2/3) move click them to the opposite direction, and then select half of the units you just selected and move them up or down that should split them.
EDIT: Stupid me i didnt realise he was moving one ling at a time. for that you click somewhere on the minimap with the control group, shift click away a unit using the unit bar on the bottom of the screen and then re-hotkey and move the new hotkeyed group back to somewhere else (back to base for example)
thats some sick marine control, if i had marine control like that i would get tank marine vs zerg every game. if that was me i would stim and watch my marines melt in big groups lol
The awsome thing about Happy's micro is that the marines are actually fighting. Lots of terran let them just run. Marines kill banelings quite fast. I wish I could micro like him though :o
Ling micro was quite useful in BW for splitting irradiates, plagues, siege tank fire and the sorts, and Day9 played BW competively as zerg for years, so he also probably had experience from that.