Theme: 40-Across has the clue: Popular zoo attraction … or a hint to 11 squares of this puzzle. Answer: Panda. Actually, it’s P and A and a rebus where the letters PA inhabit the same square.
I figured out that the trick involved a rebus of PA well before getting 40-Across. Since the PA squares are scattered throughout the grid with no particular pattern, it was an interesting challenge finding where they occur. So, this was not a quick finish. I kept plugging away over a two-day period. The southwest corner was still not filled in last night. And this is where the mystery of how the brain works came into play. I had thought the answer to 51-Down (Wash against gently) might be LAPS, but it wasn’t right. I consciously let it go, but it seems my brain didn’t. Right after I woke up this morning, the correct answer, which included the rebus, suddenly popped into my head: LA[P A]T! Once I had that, I was able to fill in the rest of that corner.