Joined at the hip.

Some days Simon and River are inseparable even when getting into trouble...

While playing with their box...

And eating their pineapple toy...

Going for a stroll around the living room...

Crashing into the arm of the couch at top speed...

Learning how to share a favorite toy...

And who could forget naptime?
For all of their differences in personality, it's funny how often they mirror one another.  Just like human siblings sometimes do.