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You may think that a dog looks cute when it rolls onto its back while playing.

But instead of being submissive, canines may be exhibiting signs of aggression, experts claim.

By studying dogs playing in pairs, they uncovered that dogs lie on their backs during a boisterous play session, not to be passive, but as either a defensive manoeuvre, or a useful position from which to launch an attack.

Down boy! The experts found that smaller dogs weren't more likely to roll over than larger dogs when playing as well as that 'most rollovers were defensive and none of the 248 rollovers was submissive'. A stock image of two very differently-sized dogs playing is pictured

Scientists at the University of Lethbridge in Alberta and the University of South Africa, Pretoria, were interested in why dogs roll onto their back while playing with other dogs, and whether it is a sign of submission, as many owners assume.

Some experts have previously suggested that the move is intended on preventing aggression, so that a dog that rolls over is submitting to a more dominant dog that is on top, Scientific American reported. 

Kerri Norman, lead researcher of the study, which was published in the journal Behavioural Processes, examined 20 YouTube videos showing dogs playing together, half of which were play sessions between similarly sized dogs and the other half between canines of different sizes.

She also set up 'staged' play sessions where a medium-sized female dog was paired with 33 dogs of different breeds and sizes, and their play observed to see whether rolling is actually 'executed tactically for combat purposes'. 

Scientists have discovered that dogs lie on their backs while playing with as a defensive manoevure or a useful position from which to attack. This graph shows the percentage of rollover types. The grey bars show play seen in person, and the white bars, behaviour observed in YouTube videos

Firstly, her team discovered that not all the dogs rolled over during play and in the 33 staged play sessions, only nine of the dogs rolled over. 

A total of 27 out of 40 dogs rolled over in the YouTube videos and the action didn't seem to depend on the size of the dogs playing together.

The experts looked for signs that the manoeuvre was linked to submission, with smaller or weaker dogs becoming passive, for example.

They also studied whether the action is part of interactive play, which proceeds a dog lying on its back 'launching an attack (offensive), evading a nape bite (defensive), rolling in front of a potential partner (solicitation) or rolling over in a non-social context (other).'

They found that smaller dogs weren't more likely to roll over than larger dogs.

They also discovered that: 'most rollovers were defensive and none of the 248 rollovers was submissive.'

In fact, none of the dogs that surveyed rolled over in response to aggressive behaviour by another canine to become passive, or submissive.

Instead, rolling dogs used their position to block playful bites and launch attacks on their partner.

The researchers concluded that while dogs may roll onto their backs out of fear in some scenarios, when they are playing, the move can be used to give them an advantage when 'fighting' back.