Let the dog sniff their hand first, and then they can give a little scratch behind the ears. (topdogtips.com)
When your dog sniffs your hand, or touches it, praise the dog and immediately offer a treat. (tulsapetsmagazine.com)
First, they measured nasal airflow during the task and found that subjects were truly sniffing their hands and not just lifting them to their nose. (sciencedaily.com)