Johnston's lawyers contend that the second drug in Missouri's three-chemical sequence may render Johnston completely paralyzed but fully conscious and susceptible to pain. They say that the chemical, which has no anesthetic properties, could enshroud Johnston in a "chemical veil" -- leaving him unable to move, cry out or communicate in any way as he slowly suffocates, "consciously [suffering] an excruciating painful and protracted death."The chemical, pancuronium bromide -- known commercially as Pavulon -- is a muscle relaxant commonly used to immobilize patients during surgical procedures. In Missouri and most of the 30-odd states that execute criminals by lethal injection, Pavulon is administered after an initial dose of the short-acting barbiturate sodium pentothal. The two drugs are followed by an injection of potassium chloride, which causes cardiac arrest."The worst-case scenario is that you wake after a sub-anesthetic dose of sodium pentothal. [You've already received] a paralyzing dose of Pavulon -- and experience the torment of suffocation and conscious paralysis -- and then the agony of the burning potassium chloride," says Mark Heath, an anesthesiologist at Columbia University Medical Center in New York. "There are abundant examples of people who wake up in the middle of surgery feeling everything -- having the full experience of pain and terror, but [because of the Pavulon] are unable to communicate in any way that they're awake."