Working K-9 Association of Central PA (WKACP) members showed the abilities of several dogs. Here is a brief excerpt of a longer demonstration given by Craig Bohren and his Australian shepherd Dart.
Before the clip begins, Kris Hopkins placed several toys that she had touched on the ground. Craig briefly handled one toy, which Kris took with a pair of tongs (so as not to leave her scent on the toy) and placed it among the others.
The clip begins with Craig indicating to Dart that Dart should bring back the toy that Craig touched.
You might note the soundtrack too. As distracting as the announcer is, Dart never lost track of his goal.