According the the Met Museum, coconuts were exotic to Europeans and a cup made from a coconut could be used to neutralize poisons.

Image description: Tall silver and coconut goblet with lid. The bowl is made of most of a coconut, the base, stand, and lid of the goblet are made of silver. The coconut is engraved with biblical scenes, including Samson holding open a lion's mouth. Cherubs look on and there's filigree. There are also silver rams and roman? soldiers connecting the silver base and the top of the goblet.

Found at: The Met