"They are cousins. They don't know it, but that isn't a crime against nature!"
"True."
"They are cousins."
"Yes, they're cousins."
"Ottilie is my daughter; her son is my grandson. Elly's father ..."
"Well?"
"Do reflect, Ottilie: Elly's father, my son, was Lietje's brother. Their children are first cousins."
"Yes."
"That's all they are."
"But they don't know that they are cousins. Lietje has never been told that she is your daughter. She has never been told that she was your son's sister."