Ok, so I couldn't wait till next month. Theo seemed bored.
Marie(chen) is a much younger and smaller rat than Theo is. This makes it easier for him to accept her since he is in the much stronger position, the rank is quite clear + females are usually more easy going in grouping.
Now that Mariechen is there Theo copies her moves frequently. Climbing new paths, taking shortcuts, chewing on new things etc. I hope they will grow strong as a team.
I will probably let them mate once. Rats usually feel comfortable in groups, so I will give them this chance.
I will make sure I won't end up with 20 Rats, 4 will be just fine to keep from the bundle.

