They're both pretty much non-verbal.
They're both extremely mobile, but they don't have the sense to keep themselves safe.
They both put everything in their mouths. Constantly.
They're messy eaters.
Neither one of them will keep their feet off of the furniture no matter how often I tell them.
Neither of them really listen or follow directions in general.
I have to tell them the same things over and over and over and over.
They both break things frequently.
I guess the good news is they'll both keep improving.