they're both females, they've never behaved this way. it looks like mating, but it's 100% sure they are both females.
i didn't want to intervene, but my poor girl didn't look comfortable, what should i do?
useful information:
they are 1 year and a half (there's a 3-4 month difference between them, and the grey one is the oldest). i also haven't noticed any change in their appetite or behaviour in general, only this.
they get along and really like each other.
grey one has always been the "dominant" one so this is extra unusual
EDIT: thank you everyone!! happy to know this is a lesbian household. i was worried that it could be a sign of some kind of aggression or problem developing. glad to know they're just having good fun
EDIT 2: I got told that there could actually be a problem with it getting aggressive and developing problems and fights between them. I will keep an eye on them and separate them if this happens again.