"It shows that the dog, when he believes the owner cannot see him, will become a thief in the night," Dodman added.
And that implies a fairly sophisticated level of thought, he said.
A number of studies have suggested that animals have so-called "primary emotions," like anger or joy. But those are relatively simple on the emotional scale. Whether animals have "secondary emotions" -- more complicated feelings like guilt, jealousy and envy -- is controversial.
Secondary emotions require a level of self-awareness and an awareness of others that some believe are lacking in animals -- with primates like chimps and baboons being the possible exception. But recent studies have been turning up evidence that dogs do demonstrate complicated emotions like jealousy.
"This study give us another piece of evidence," Dodman said. "They do appreciate themselves as entities; they do have thoughts and emotions. And it appears they may have secondary emotions."
Of course, people who live with a dog may need no convincing on that, Dodman noted.
Other humans, however, may well be skeptical. Kaminski said more research is needed to uncover the extent to which dogs understand their environment and the humans in it.
For his part, Dodman said he does not think dogs sit around and ponder existential questions. But they may have deeper thoughts than they have traditionally been given credit for.
"That's uncomfortable for some people," Dodman noted. "We have to admit that animals are much more like us than some people want to believe."
Learn more about canine behavior from the Humane Society.
SOURCES: Juliane Kaminski, Ph.D., lecturer, psychology, Universi
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