朽壞

朽 = 丂 + 木 : Marie Curie (xi) visits the outhouse (ou3) in late summer and finds an old rotten (朽) Christmas tree (木). In fact the tree is so rotten that she can't endure the smell and has to put on a breathing mask (丂).

坏 = 不 + 土 : In the airplane's bathroom, there is a clear sign that it is forbidden to enter the room with dirty feet. Helga Horse is quite spoiled though, so she enters right after she went to the muddy stables and spreads dirt all around.