Milk

Milk is a possible clue in Ariana's Motive. It is seen handed out by Blackpink in episode 1 and drunk by Kylie Jenner, Selena Gomez, Cyndi Lauper, Taylor Swift, Lady Gaga, and Nicki Minaj. Everyone who had drunk milk stayed alive in Episode 1.

In Episode 2, we see both Cyndi and Kylie dead in the Gold Room with milk trickling out of their mouths. Ariana notices and points out the empty glasses on the floor. However, the blood splatters in the room suggest that they may have been killed in some other way (or their bodies were tampered with after they had died). It is very probable that they were poisoned by the milk.