We tested the hypothesis that if odor fallout (the release of a human's odor onto an untouched object) in human subjects exists, then holding a hand above an absorbent will produce a detectable scent which will be subsequently matched in a detection test by trained canines. Scents were collected from seven males to sterile cotton absorbent squares. The left hand was used to get the control scent and the right hand served as the target scent. Each experimental subject was sitting; his left hand was laid down on a cotton square for 3 min. The right hand was held 5 cm above another cotton square for 3 min. The scent identification was done by two specially trained police German shepherds. These canines had routinely performed scent identification line-ups as part of criminal investigation procedures. Both canines performed 14 line-ups and correctly matched the collected scents of all test subjects. The results suggest the existence of human odor fallout, whereby a human scent trace is left by humans even if they do not touch an object.

Canine Behavior Research Center Department of Animal Science and Ethology Czech University of Life Sciences Prague Kamýcká 129 165 21 Praha Czech Republic

Canine Behavior Research Center Department of Animal Science and Ethology Czech University of Life Sciences Prague Kamýcká 129 165 21 Praha Czech Republic; Department of Ethology Institute of Animal Science Přátelství 815 104 00 Praha Uhříněves Czech Republic

Department of Statistics Czech University of Life Sciences Prague Kamýcká 129 165 21 Praha Czech Republic

Regional Headquarters of the South Moravian Region Police of the Czech Republic Zámecká 416 664 42 Brno venkov Modřice Czech Republic

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Ability of dog owners to identify their dogs by smell