We tend to keep small things on the right side of the stairs when we use them a lot there (ie. Marty cleans his tennis shoes or puts on a brace for his peripheral neuropathy) or when I'm too lazy to take something up - such as shampoo I bought - I'll just pick whatever it is up as I go upstairs.
The felines have a habit - and I think this is Whimsy - of leaving their mice along the left side of the stairs. I posted the pic on FB if you're on there.
I realized this was mimicking behavior - kind of like parallel play.
Gosh--they get more adorable by the day.