Table 1. Description of the 40 video clips showing dog behaviour and the corresponding possible interpretation(s).

The twenty video clips that received the most extreme scores on the difficulty ratings after scanning are marked with a cross in the column ‘easy’ (10 clips with the lowest scores) or ‘difficult’ (10 clips with the highest scores). In the fMRI analyses, brain activation during the observation of these ten difficult video clips is compared with brain activation during the observation of these ten easy video clips. Some video clips showed the same behaviour. For example, there are two video clips that showed a dog drinking water. When this is the case the number of video clips showing this behaviour is reported between brackets.

	possible interpretation(s)	easy	difficult
Description of the behaviour shown in the video clips
rubbing the neck against the ground	scratching put a smell from the ground onto himself		x
placing the mouth over the mouth of another dog	showing dominance
eating leafs	to promote digestion
making a hole in the ground	digging, searching something		x
wiggling the tail and looking up	the dog expects something from the person in front of him
smelling at a tree and marking	the dog marks the tree
scratching on a blanket (2)	creating a place to sleep
turning in a circle and laying down	creating a place to sleep
walking and suddenly freezing	orienting response before going after something
scratching at the end of the couch	dog is afraid to jump off the couch		x
turning on the back	scratching		x
covering something with earth	after urinating, covering it with earth		x
two dogs look at something, then one attacks the other	something interesting catches the attention of the dogs, then the attacking dog claims it		x
standing up and sniffing	there is something that is held above the dog that the dog wants	x
running away, tail is first upright and then it goes down	first the dog has a dominant pose, then the dog walks away		x
laying before a nut and then eating it	the dog waits for a command to eat the nut
sitting up straight and still	the dog hears something
eating grass	to promote digestion
licking the ground	the dog has smelled something and then licks		x
two dogs sniffing at each other's back	to meet each other
licking at the paw	Washing
eating dry dog food	Eating	x
chewing at a bone	Chewing	x
drinking water (2)	Drinking	x
scratching (2)	Scratching	x
sniffing at grass	Smelling		x
shaking out	shaking out
sneezing and then showing the teeth	sneezing and then showing dominance		x
two dogs smelling at each other's noses	to meet each other
Sleeping	Sleeping	x
stretching the corps	stretching after sleeping
Barking	barking because something interesting has happened
walking at the leash and yawning	walking and yawning (because of fatigue or stress)
lying in basket and yawning	yawning because the dog is tired	x
licking the back	Washing	x
tearing at the leash	the dog does not want to walk
a dog is lying down and wheezes	resting after an effort