A pet yukkuri making children without her owner's permission, either between 2 pets or between a pet and a stray. Often leads to abandonment, abortion or psychological abuse where their children is tortured and killed in front of them.
Since yukkuris have very limited level of intelligence, ability to "defecate" memories out of their bodies, and considering the fact that having children is coded to their brains, yukkuris, even the ones with silver and gold badges often commit this act which often results above consequences for them.
Silver and Gold badge tests especially focus on this aspect of yukkuri training as significantly trained and intelligent yukkuris are required to obey their owners without question and do not over populate the house with children. It often fails.
Tag is also used for gutter trash where it's shown or implied that they're abandoned pets which was abandoned because they refreshed without permission.