It is rumored that the Buddha's last meal, which brought about a sharp decline in his health, was either pork or tender food loved by pigs (Mahaparinirvana Sutra). Mushrooms would fit this description and could have easily and unintentionally been toxic. Surely the blacksmith was trying to provide the best gift he could to a famous teacher and his renunciate disciples.The Buddha saw that there was no other being, seen or unseen, who could possibly digest the food offered to him by the blacksmith Cunda. He had already relinquished the will to keep his body going, and this meal made it possible to bring the material basis of his dependently-originated becoming on Earth.
Most Buddhists (Chinese Mahayanists) have been vegetarian in consideration of developing compassion. No particular diet is a Buddhist requirement (although many types of meat, such as bear, are specifically excluded). But as the world has moved toward Western ideals of luxury, affluence, and poor health, meat eating has increased.
Hygienic practices have not kept up, even in America which seems to do the most to promote the cruel practice of not only slaughtering and eating animals (more than a million a day being killed for consumption in the US alone). For all the improvement in sanitation, we have not managed to eradicate trichinosis, salmonella, food poisoning, or worms. This easy vermifuge test may be performed to check the status of slaughtered pigs ingested by careless human carnivores.