After Lugia had left, the other succubi began reprimanding Seraphine for her passivity in the negotiation and how she had let Lugia manipulate her. Succubi are truly the most loyal beings to the gods of Eros, so seeing that their leader didn't get information about Andrew frustrated them, as they wanted to meet their new master as soon as possible.
Despite her sisters' complaints, Seraphine didn't get upset and smiling, she responded, "How would you have pressured her?" To which the other succubi immediately replied, "With force, we would've forced her."
Hearing her sisters say they would have forced Lugia to talk, torturing her and doing many other barbaric things, Seraphine couldn't help but burst into laughter. Seraphine wasn't mocking them; their ideas genuinely amused her, but the other succubi didn't see it that way, they pouted and scolded her.