Photos Show Dog And Rat Sharing The Sweetest Little Friendship

<p><a href="">Instagram</a></p>
<p><a href="">Instagram</a></p>

Friends come in all shapes and sizes - and to prove it, here are two pals who really couldn't be more different.

The unlikely friends live in Chicago, but have since captured the hearts of folks around the world on Instagram.

Pretty much everyone agrees they're the cutest BFFs ever.

While Osiris, a 3-year-old Dutch Shepherd mix, towers over his little companion Riff, a 3-month-old fancy rat, it seems the size of each other's heart is what matters most to them.

Riff loves showing affection to his big furry friend ...

... and the feeling is mutual ...

... because theirs is a relationship built on respect, caring - and trust.

Can a lovable dog and rat duo help change the world? Their adoring human certainly thinks so:

"Seeing them care for each other and have such an unexpected friendship gives me a tiny bit of hope for the rest of the creatures on this planet - especially humans :)"