Watch As 'Reactive' 143lb Dog Falls in Love With Baby Sister in Sweet Clip

A video of a dog "obsessing" over his canine sibling has gone viral on TikTok, where it received 827,500 views at the time of writing.

The clip, shared by TikTok user @sheridanratko5, shows a montage of interactions between Rocky and his sister Marlow.

The video was shared with a caption that read: "Watch my 65kg [143lb] reactive dog fall in love with his sister. The first month of owning Marlow was highly stressful with Rock obsessing over her & Luke working away [tearful laughing face emoji] #rockyandmarlow #rocky #marlow #reactivedogs #littlesister #puppy #reactivedogawareness #reactivedogsunite #hisreactivenotaggressive."

A reactive dog is dog that overreacts to certain stimuli or situations.

In an August 2020 article for the American Kennel Club, the world's largest purebred dog registry, veterinarian Erin Rakosky explained: "Genetics, lack of socialization, insufficient training to learn self-control, a frightening experience, or a combination of these can cause reactivity, and fear is typically the driving force."

Reactivity is often confused with aggression, which is defined as "hostile, injurious, or destructive behavior toward an individual, whether human or another animal," the veterinarian noted.

As touching as the bond between the sibling pair in the latest video may be, can dogs really be best friends?

In a May 2018 article for PetMD, veterinarian Dr. Wailani Sung said: "It is not an uncommon finding to see pups extend dog companionship to preferred playmates and also have other dog friends [to] hang out with, very similar to human behavior."

Sung said some dogs prefer a certain style of play and regardless of the location of their play—be it a dog park or someone's house—dogs "gravitate more towards other dogs that play similarly."

According to the veterinarian, dogs that are best friends prefer to stay in closer proximity to each other and ignore other dogs. Dog besties tend to play more or spend more time in general with each other and may be more open to sharing their toys, bed, water bowl and general space, Sung said.

On the website of VCA, one of North America's largest animal hospital chains operating over 1,000 animal hospitals, veterinarians Dr. Ryan Llera and Dr. Lynn Buzhardt said: "Most dogs will welcome a new sibling, but it is not always smooth sailing. The furry family member you have now will face many changes when a new dog enters the picture and may feel a bit displaced. He may not like sharing his territory, toys, food, resting places, or humans."

So, before you introduce a new dog in the home, it's important to consider what type of dog will fit in with your family as well as the logistics, such as the following questions, as outlined by Llera and Buzhardt:

• Does your home and yard have space for another dog?
• Do you have a large or small dog, and do you want to add a large or small dog?
• Do you have time to walk, feed, and play with another dog?
• Can you afford the additional expense of caring for another pet?
• Is your current dog physically able to interact with a pup or would an older, calmer dog be a better canine friend?

The viral video shows various moments of playful interaction between the two dogs, from running around on a grass field and play fighting in the house to snuggling up together while sleeping on the floor.

The original poster said the two dogs are "obsessed with one another two years on" and "would be lost without one another."

The owner said initially the pair were kept separate for about a month but were walked together every day. They "started apart and got closer every day," the original poster said.

Several TikTokers were delighted by the dog siblings in the latest video, with some feeling a sense of hope for their own reactive dogs.

In a comment that got 1,189 likes, user roseroyce12 said: "Thanks for sharing, especially the harder parts, this gives me hope that my beautiful reactive dog may get better with time and patience."

In a comment that got 1,022 likes, Zoeh wrote: "Now THAT is the perfect example of amazing dedicated owners [red heart emoji]."

Danette Mendryk: "Thank you for sharing the hard parts of having a reactive dog. This past week has been a struggle with my dog and this gives me hope."

J E S S simply wrote: "So beautiful!!!!! [red heart emojis]," while Jess unsworth said: "Melts my heart [teary-eyed, sad face emojis]."

Newsweek has contacted the original poster for comment. The latest video has not been independently verified.