What do you think?

I have just noticed something very... bizarre. i have two friends let's call them koala and hamburger, well today it really, really, clicked that they look, draw, and act very, very, very similar. it weirds me out a little 'cuz they've been like this for about 4 or 5 years now...
here is a sample of their diff artworks -

Hamburger -

and here is koala -

   

notice any similarities? I digress that there are distinct differences, but the similarities are also quite distinct.