Yesugai the Brave, by various accounts, was poisoned at a meal on the steppes, by Tatars who by custom owed even an enemy hospitality.

We do not know if it was actually poison. This could have been a simple bacterial infection. However, actual poisons were available, such as from poisonous mushrooms.

Fecal matter would have been a hit-or-miss matter, depending on the local pathogens and whether Yesugei Baghatur had been exposed to them in the past.