Domino circuit

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A domino consists of two squares, each with some number of dots between 0 and 6 in each square. A standard double-six set of dominoes contains exactly one domino with each possible pair of numbers on it. Suppose you start laying down a line of dominoes, observing the rule that two dominoes can touch only if the numbers on the touching squares are equal. After laying down all but the last domino you notice that the two ends happen to have 3 and 5 dots respectively. What does the last domino look like?