興味深い

1. Origins, structure, and basic meaning

• Structure: 興味深い (きょうみぶかい) is an i-adjective meaning interesting or thought-provoking.
• Basic usage: 興味深い仕掛け modifies exhibit mechanisms; 違いが興味深かった gives a past evaluation of a difference.

2. Common pitfalls and similar expressions

• Attributive form and past 興味深かった
  • The nonpast form directly precedes 仕掛け, while past predication replaces final い with かった.