What theory of liability did Justice Posner use in finding the defendant liable?

Wedge v. Planters Lifesavers

What theory of liability did Justice Posner use in finding the defendant liable? What are the judge’s reasons for reversing the decisions of the lower court? Do you agree with the decision? Why or why not? 

Here is a link to the case

http://openjurist.org/17/f3d/209/welge-v-planters-lifesavers-company

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