Riddle me Murder

Two pills

I woke up to a glaring light. I was in a dark room with a dirt floor. In the corner there was a shovel.

In front of me, there was a metal table. The table had a jar of pills on it- probably poisonous.

Jason saw me open my eyes and sat down in front of me. He placed two glasses of water on the table- one for me, and one for him.

He sat down in the chair opposite to me and explained: "Take any two pills from that jar. Half of them are poisoned. You choose which one to take- and I'll take the other. Understood?"

I nodded my head. Something about this just wasn't right. I chose two pills from the jar, one purple and spherical, the other red and flat.

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I placed the pills on the table. "You will take the purple pill," I said, nudging it slightly in his direction. The pill rolled off of the table and hit the floor.

As Jason reached to pick it up, I switched our water glasses. It was the one good chance that he would die instead of me. The water had been poisoned. That must be the answer. If he did this to all of his victims, and he survived, then surely the pills weren't poisoned.

He sat back down in his seat and brushed off the pill. "Ready?"

I nodded and placed the pill on the back of my tongue. I took a huge swig of the water and swallowed, the pill scratching down my throat uncomfortably. He did the same.

His mouth began to foam as he coughed and vomited. It was the most disgusting death I could have seen. As he died, he placed the key to the room in his mouth and somehow swallowed one last time- thus trapping me in this room. Then, he sputtered out a cough- or a laugh- and died.