Puzzle (Who Invented Facebook’s Like Button)

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Across
  1. 4. (adj.) - Complicated and difficult to understand
  2. 6. (v.) - To try to find more information about something
  3. 9. (n.) - Someone who is the first to discover or develop new methods
  4. 11. (v.) - To gradually spread through a group
  5. 12. (n.) - A cause of continual troubles
  6. 13. (v.) - To ask for money, help, or information
  7. 14. (v.) - To discover or guess something
  8. 15. (n.) - Something very attractive or hard to resist
Down
  1. 1. (n.) - An unexpected source of something pleasant or useful
  2. 2. (n.) - A brain chemical involved in motivation and reward
  3. 3. (n.) - The occurrence of making fortunate discoveries by chance
  4. 5. (v.) - To think about something in a casual way
  5. 7. (v.) - To combine to form one single group
  6. 8. (v.) - To make someone do something by persuasion or reminder
  7. 10. (n.) - The general spirit or feeling of a period in history