411 REFERENCE · Wikibooks
Chess Opening Theory/1. e4/1...c6/2. d4/2...d5/3. Nc3/3...dxe4/4. Nxe4/4...Bf5/5. Ng5/5...Bg6/6. N1f3/6...h6/7. Ne6/7...fxe6
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Black recaptures the "free" knight. But actually it's not completely free, and black will pay even more for thinking less.