The joke that always gets me is the scene in Duck Soup when Groucho is trying to "prove" that Harpo isn't a reflection. When Groucho spins around, the workaround Harpo comes up with is genius. I absolutely love that they were smart enough to make that joke back then.

He apparently lived pretty close to Groucho, and he'd regularly welcome Groucho's daughter into the home.

There's a You Bet Your Life clip where Harpo makes a surprise guest appearance to promote his book. Groucho isn't exactly thrown off his game, but you can tell he's genuinely happy to see his brother.

One last story that I guess is a little bittersweet but speaks to how sweet and happy Harpo was, evidently Chico was a compulsive gambler. Someone once asked him "how much money do you think you've lost over the years just from gambling?".

Chico said "ask Harpo how much money he's saved over the years and you'll have your answer."