Selective ability to memorize

Dd7 has watched the movie Barney: Jungle Friends twice in the last few days. As far as I know, she never saw the movie before this week. Now she is singing songs from it that she memorized after just two viewings. WHY, oh, WHY, are we still struggling through addition drills together every morning? There needs to be a Barney (or Blue's Clues or Disney) movie with songs on all the basic addition facts! She'd have them learned in a jiffy with little effort and struggle.