Hurst, J. L., Fang, J., Barnard, C. J. 1993. The role of substrate odours in maintaining social tolerance between male house mice (Mus musculus domesticus). Animal Behaviour 45, 997-1006.

The group's odor cues protects the individual group member from being attacked. Strangers who do not have this group specific odor cue are attacked.It may be good advice to always leave some soiled bedding to assure group harmony in the cleaned cage.