sometimes we inject substances that change or damamge the dna/gene of a mouse so that we can study the effects and try to correct them with remedial substances. sometimes we expose the mice to small amounts of radiation so that it kills off the cells in their bones, we then replace the cells in the bones with ones we want to study through a tail vein injection and over time see how the cells we introduced repopulate the mouse. Sometimes we inject substances they create an immune response like when someone is allergic to pollen or peanuts for example and then see how the body copes. In my facility we are not looking at a mouse natural behaviour but how its body functions at the molecular/cellular level. Being in a lab does limit the amount of natural behaviours a mouse can display but we try our hardest to allow them to live as much like they could in the wild; examples include making sure they live in groups, providing toys and enrichment and feeding them all the nutrients they require to be healthy.