She's seen just standing and staring at her sister's bed, unmoving, for about a minute and she doesn't wake up until her mom comes into the room.
No one wants to wake up to that terrifying sight. It's not even that she's staring, which is creepy on it's own, it's that she doesn't even flinch - even when her sister is screaming at her and crying while begging her to stop...
It is not that uncommon for a man to come home and find his wife in bed with another man. However, the plot thickens immensely when the other man happens to be a close family member.