There's nothing better than seeing a rescue dog settle into their new home—especially when they come out of their shell and begin to thrive.

Take this one-eyed dog, Theodore, for example. He has gone viral on TikTok for acting like a "puppy," despite being 12 years old.

The video, shared on September 7 by his owner @care1249, has garnered over half a million views (552,700 at the time of writing).

An excerpt from the caption states that while Theodore may be old, he reminds his owner of a "baby gremlin" and doesn't shy away from bossing her around until she throws toys for him.

What makes this video even sweeter is the fact that Yorkshire terrier mix was saved from euthanasia, as mentioned in another clip. Judging by his energetic behavior, he wasn't ready to be put down, and it's clear that he's happy in his new home.

Sadly, not all shelter animals are as fortunate. The American Society for the Prevention of Cruelty to Animals reports that around 390,000 dogs and 530,000 cats are euthanized each year. This is a significant decline from approximately 2.6 million in 2011, as more people are choosing to adopt from shelters rather than purchase from breeders.

Often senior dogs like Theodore are overlooked, but they shouldn't be, according to dog owner Adrian Lott. He previously told Newsweek why he thinks senior dogs should be considered.

He said: "I love old dogs, because they tend to be a little lower energy, need less exercise, and you can focus less on training.

"A lot of seniors just want a warm, cozy, happy home to hang out in until it's their time. Senior or older dogs are great dogs for newer pet parents, because they are more or less settled in their personality. The cherry on top is that you're helping a dog who really needs it."

But adopting an old dog isn't for everyone, according to the comments section of the clip that has more than 150,000 likes.

One user said: "No, I'd cry every single day knowing I wouldn't have a full 10 [years with] him."

Looking at the bright side, Theodore's owner said: "It also really makes you appreciate the present moment. I plan to make him a bucket list."

She also agreed with another user who said: "We call ours 'the forever puppy.'"

"He must've spent a long time without being able to be his true self. He's the cutest," said a fourth user.

Newsweek reached out to @care1249 for comment via TikTok. We could not verify the details of the video.

Do you have funny and adorable videos or pictures of your pet you want to share? Send them to life@newsweek.com with some details about your best friend and they could appear in our Pet of the Week lineup.