jmm and Sigman:
The "Do not eat" exhortation is a modern continuation of the tradition of ancient taboos propagated by most cultures against eating kidneys and livers. This was an excuse for these relatively tender meats to be surrepticiously horded and eaten only by the older tribal headmen with fewer or bad teeth.
Silica gel can only be properly eaten by senior union, corporate, governmental officials and by tenured repeat groupies favored by prominent rock bands.