When does a mousetrap have zero elastic energy?

Stamatis and I gave a final question involving the energetics of a mouse trap car. A student came up during the exam and asked, 'should we assume that the mousetrap has zero elastic energy when it is fully sprung?' I was impressed by the insight of this student and the fact that neither Stamatis or I had reflected on this point in writing and reviewing the question. In fact, the Physics Teacher article that we quoted in the question says 'just as the arm arrives at its most forward position, when all of the spring potential energy has been expended...' But as this student clearly recognized the spring of a fully sprung mousetrap still has elastic energy to give.

Thank goodness for student insight and for Stamatis who will be grading this question.