If you want to play with chemicals, carbon monoxide is way too merciful. Sure, if you place them in a glass chamber you can watch them slowly suffocate, but if you're making a point of making him suffer, try sarin, or organophosphate, or maybe even a large amount of mustard gas for immediate effect. The best part is that sarin and organophosphates are legal chemical pesticides, so no one would suspect you're out for torture/murder when you're innocently purchasing a few gallons of the stuff.
My room is an insane asylum, and I am the patient.
Beware of Dog signs are overrated. Beware of Writer.
Warning! Crappy author at work! Any hapless bystanders/passerbys will be sentenced to an eternity of hell by eye-hurt :3
