No one will ever be as happy to see you as man's (or woman's) best friend -- no matter the dog's age. It doesn't even matter how long you've been gone or how often it happens, a pup will always display unbridled joy and excitement as soon as you walk through that door.

Buddy's Heartwarming Welcome Back

When Army private Hannah Foraker and her 13-year-old Golden Retriever Buddy got reunited after over three months, the elderly was as joyful and excited as a young pup. The pair of best friends shared a heart-warming moment seen in the short video that Foraker uploaded on YouTube. The video already has more than 2 million views.

"Buddy was so overwhelmed that she just collapsed in pure happiness," Foraker said in an email interview. "We were apart for [more than three] months, so the reunion was such a beautiful experience."

Now a biomedical equipment specialist in San Antonio, Texas, 21-year-old Foraker said goodbye to her four-legged friend back in September to embark on a basic training program at Fort Sill in Oklahoma. The 10-week training was challenging for the sheltered Cleveland native and she described it as a "character building experience" that's one of the hardest things she has ever gone through.

Part of the difficulty was being apart from her childhood pet and best friend Buddy. The two grew up together and spend most of their time together bonding over camping, swimming, hiking, running through backyard obstacle courses and more.

So, Why are Dogs So Happy to See Humans?

Those who are not familiar with dogs will find their reactions to a family member arriving at the house jarring and over-the-top. Even people with ample experience do not know exactly why their pets get so excited every single time.

Although the particular greeting depends on a lot of different factors including temperament, personality stress and self-control, one of the reasons for the dog's joy is that the separation from their owner is often involuntary and -- from their perspective -- without good or clear reason.

University of Trento neuroscientist Giorgio Vallortigara pointed out that detachment from their pack is not in the nature of dogs saying, "The exaggerated level of greeting that can be observed in some dogs is likely due to the fact that they have not yet learned to accept the possibility of non-voluntary detachment."

"This dog probably had a pretty boring day without much enrichment, and moreover may have been alone all day, which is unpleasant for a social animal," Jessica Hekman of DogZombie blog also explained. "So in addition to being glad to see us, they are probably feeling some relief that they will get to do something interesting, like go for a walk, and have someone else around."