WARNING THIS WILL RUIN THE ENDING:
When Shrek gets sent off by that short (height wise) Lord, to rescue the princess from the dragon, so Shrek can get his swamp back, it's nighttime when Shrek finally rescues the princess. Later Shrek (and the audience) find out that the princess had a spell cast on her by a witch and during the day she looks like a princess, and at night she looks like a female oger. Now if at night she looks like a female oger, why didn't she look like a oger when Shrek rescued her? It just puzzled me.