I watched this again and noticed some things.
Wilder may have put more thought into it than I realized on the first viewing.
Every time Teddy thinks of Charlotte a sound of a seagull is heard. I noticed it the first time, but it didn't make sense. Seagulls sounds make me think of the beach. This movie doesn't show a beach. When I watched it again, it hit me that the opening credits are pretty much from the point of view of the seagull that lands on the ledge beside Teddy.
The only thing - this scene occurs after the rest of the movie chronologically, so why would the character associate the seagull sound with Charlotte when he hasn't been on the ledge yet? I guess it means it is really for the viewer?
I spotted 2 hearts in the film. Maybe there are more.
The first is when Didi (the wife) shoots the gun and Teddy holds up the underwear. It looks like a smoking heart to me.
The second is at the end. When Teddy is on the ledge and looks down at the fire truck ladder. If you look at the tree it looks like a heart. Not sure if that was intentional.

And zoom in for extreme close-up.

They should slo-mo on the bush.

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