So, you know that sense of satisfaction when you've just finished cleaning something? No? Me either, but, this woman certainly does.
Apropos of nothing, here's a recent paper on sperm competition in Drosophila.
Yeh SD, Do T, Chan C, Cordova A, Carranza F, Yamamoto EA, Abbassi M, Gandasetiawan KA, Librado P, Damia E, Dimitri P, Rozas J, Hartl DL, Roote J, & Ranz JM (2012). Functional evidence that a recently evolved Drosophila sperm-specific gene boosts sperm competition. Proceedings of the National Academy of Sciences of the United States of America, 109 (6), 2043-8 PMID: 22308475