A new knowledge entered the life of the man ie. the knowledge of sin..
This and other knowledge as well disturbed the natural purity of mankind. This proves true the words of the Wise Solomon, "..he who increases knowledge increases sorrow" (Eccl. 1:18)
Perhaps the first thing which Adam knew was being a man and Eve a woman... Sexual knowledge began to penetrate his mind, then his feelings.. He recognised that sex is something shameful and so he began to cover himself.. Then he knew fear and tried to hide himself behind the trees..