US student's arm goes numb after drinking hot water, colleagues find out why. A US university student experienced a numbness in his fingertips and his left arm after he drank hot water. He discovered a white powder near his water container, after which his academic peers tested the substance and found that it contained 'acrylamide', a neurotoxin. Later, his colleague, Aili Wang, a Chinese national, was caught for allegedly administering him the substance.