Final answer:
The disappearance of Moussa's donkey prompts Bouki to speak with Toussaint about renting a horse.
Step-by-step explanation:
The event that most directly prompts Bouki to speak with Toussaint about renting a horse is the disappearance of Moussa's donkey. This event is significant because without the donkey, Bouki is unable to transport his yams to the market. Bouki realizes that he needs a horse to carry his yams instead, leading him to approach Toussaint for a solution.
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