Scheme showing examples of how the scent identification line-ups were performed.

<p><b>1A</b> is a scent of the first twin and <b>1B</b> is a scent of the second twin of the same pair. The blank rectangles stand for the distracting scents. An interrupted line signifies that the dog alerted to the scent. <b>C</b> is a control scent or training scent used by the handler for training purposes to let the dog make positive matches. The dogs moved from left to right. The separated rectangles on the left represent starting scent. In the first line-up, a twin's scent served as an attractor in a control line-up. Any given dog smelled the starting scent and was sent to search for the matching scent, while ignoring the attractor (top). A correct result of the middle line-up would be “not matched” i.e. the dog did not match the two scents. The bottom row shows matching of two scents collected from a single twin. In this case the correct result would be “matched” as required.