What is the liability if a passenger promises to guarantee the value of another's goods if thrown overboard?

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If one person tells another to throw their goods overboard saying, 'I will guarantee it,' or 'Its value is upon me,' then the guarantor becomes liable for the value. This liability arises because the guarantor caused the loss of the owner's property for a beneficial purpose, thus the compensation is due from the one who undertook the obligation, similar to guaranteeing the price of a freed slave.