[Xuzz]

But your two cousins, who may have smartphones, could both have your grandmother as a shared friend — and thus, since they were both connected to you and were connected to your grandmother, Facebook assumed you might know your grandmother?

[lucb1e]

Good idea, but I thought of that. They don't have my grandmother as shared friend (she's from the other "side" of the family as we call it, not sure if that's proper English).