I was reading this question about Falcon 9's re-entry Max Q, which states that the Falcon 9 has a re-entry pressure 3 times higher than during launch.
I was shocked, because SpaceX takes precautions against launch Max Q — specifically a conical fairing. But during re-entry the leading surface is less than aerodynamic — the 9 engine bells are basically sails. I'm surprised they don't get torn off during re-entry, but not only are they still there, they're usable!
What does SpaceX do to protect the Falcon 9's engines during re-entry?