What is the Technique?

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Across
  1. 6. Vivid pictures created by words
  2. 7. This homework is going to take years to do!
  3. 8. Dot dot dot
  4. 10. The stars danced in the midnight star
  5. 11. A symbol repeated throughout the text
  6. 12. Fair is foul, and foul is fair
Down
  1. 1. Buzz, Oink, Boom, Splat
  2. 2. The pilot had a fear of heights
  3. 3. Chocolate is my Achilles heel
  4. 4. A sign representing something other than itself
  5. 5. She's a real firecracker
  6. 9. They fought like cats and dogs