Mouse studies often fail to replicate in surprising ways. Let me enumerate some of the ways: 1. Mice handled by male scientists feel less pain. The finding holds true when a female scientist does the experiment but holds a t-shirt, previously worn by a man, near the mouse. The effect fades after 30 minutes. 2. Mice spend less time licking an irritated part of their body when a human is nearby, “even if that ‘person’ is a cardboard cutout of Paris Hilton.” 3. Mice raised at five different animal facilities in Europe, under otherwise identical conditions, had “persistent differences in body weight” and behavior. 4. If two different scientists at the same university carry out the same experiment on mice, their results will be MORE replicable than if the same exact experiment were carried out by the same person at separate universities. 5. Mice that give birth in cages with little toys or knick-knacks produce more pups. Those pups are larger after 21 days. 6. “Mice housed on deep bedding had smaller adrenal, kidney, liver and heart weights as well as larger body and tail lengths compared with groups kept on shallow bedding” after just 12 weeks, according to one study. 7. Animals stored on higher shelves are more stressed and have impaired immune systems, probably because these areas are closer to lights and vibrate more. Mice on the top shelf of a rack receive 20-80x more light than mice housed at the bottom. 8. Mice exposed to even dim light during the night (e.g. an LED on a computer monitor) “had a body mass gain…about 50 percent more than other mice that lived in a standard light-dark cycle.” 9. After just four weeks, mice exposed to a dim light during the night ate more than those in complete darkness. (Mice, like humans, raid the proverbial refrigerator when they can’t sleep.) Many genes linked to inflammation were also activated. 10. Mice kept in cages with wood chip bedding eat about 1.5 grams of their mattress every day. This changes the bacteria in their microbiomes. 11. (Not about replication, but) about 80% of drugs are tested only on male mice. Even though some drugs, notably Ambien, are more potent in females and cause more side effects. 12. About 6% of all mouse genes are regulated in sex-specific ways. The expression level of more than 1,000 genes varies between males and females, and the level of another 600 genes wobble, up and down, during a female’s estrous cycle. 13. Grain-based food usually contains unknown amounts of phytoestrogens, which change the onset of an animal’s puberty. 14. The standard diet for mice, called AIN-93, hasn’t changed in 30 years. But manufacturing of that food HAS changed: Even if you use “the same grain-based diet used in the past by others, its composition will likely differ.” In other words, the same food used in mouse studies today vs. the 1990s is different, even if its name is unchanged. 15. Mice exposed to a regular, 37 Hertz magnetic field spend less time exploring open spaces, and more time sleeping. 16. Mice are kept in rooms between 69 and 79 degrees F. “But the natural comfortable temperature for mice is warmer — between 30 and 32 degrees Celsius (86 to 90 degrees Fahrenheit).” Colder mice experience more stress, their tumors grow faster than mice kept in warm rooms, and “mice genetically modified to develop obesity only gained a lot of weight at warmer temperatures but not at colder temperatures.” All links at source below. These studies make for fun reading materials.