Extractor Trick
From Liquipedia StarCraft Brood War Wiki
The "Extractor Trick" is a technique employed by Zerg users in order to temporarily exceed their supply limit and get an extra Drone or pair of Zerglings before having to make their first overlord.
Description[edit]
At 9 control and approximately 70-80 Minerals, send a Drone to build an Extractor, reducing your control to 8. Immediately build a Drone, raising your control to 9. At this point cancel the Extractor, which will return your Drone, leaving your control at 10/9.
Uses[edit]
This trick is best used when going for a 9 Pool build. In this build, the 10th Drone would not normally be produced until after you finish producing Zerglings, giving you an extra Drone for a significant period of time.