She knew.
There were a lot of bottles in the laboratory and Arya managed to see it through the surveillance as the International Agents Association brought them out along with the police officers.
Through scanning them all, Arya knew which one was the one that the man drank and the number of these bottles… were only two.
There were many similar batch around it but only two bottles were special and if they paid close attention, they would see that the color was different. She didn't know what materials they used, but she knew that only two were the most similar to the one that the man drank.
There should be a special materials used in these three bottles.
But this batch of research did produce a lot of bottles, which was taken by several forces and many of the bottles were smashed several times.
Of these two special bottles, Arya saw that one of them was smashed and the other one…
It was nearby.
