The Doctor Says, "He's Shaking All the Time, Yo"

Rice died of old age and extreme nervousness, which i have seen on many death certificates. Nervous prostration is interpreted as extreme exhaustion. If he got indigestion from mercury poisoning, it's possible tha he did get enough mercury in his system where he's developed a level of the shakes in his hands. Generally, mercury, when it starts affecting the nervous system, affects the upper extremities before the lower extremities.