If zerg reacts perfectly the zerg gets ahead. This is often the case for pylon blocking zerg expansions in ZvP as well but many people don't realise this because most zergs screw up their reaction. As people have said above, just use 1 drone to kill the scv and keep building drones and your pool in your main. IF the ebay or whatever only getrs like 50-100hp then sometimes its worth it to break down with 2 drones. However usually its best to just wait for lings, get a faster queen, and you're on pretty much the same larva, maybe 2-3 less.
The reason is a Queen produces 4 larvae/40seconds. A hatchery produces only 3 larva/45 seconds. Therefore having your queen on your main faster and having a queen ready for your natural the MOMENT it finishes negates much of the lost larva in the large delay on your expansion.
Most common mistake is THINKING about how to respond ingame. If you ever have to think about a response in game I can guarantee you you aren't macroing while you're wondering what to do. Remember next time the moment you see it:
1) attack scv with 1 drone
2) Build pool
3) build overlord and keep building drones
Normally people idle on 3 larva for ages and bank alot of resources because they get confused.
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