For the ones saying "how can she not know?"
Folks... the 3 leg duche only did it with her when he was horny or she was ovulating, and by what was told in ep 2 or 3, he inserted himself on her feom behind, pleasure himself and then leave.
Ofc she can't "understand" his body.
The 3rd leg she might recognise tho.. cuz.. sis... that's not thing u forget in ur life lmao