Or "Knock knock!"Actually it was the engine cowling that departed the aircraft. It's job is purely aerodynamic: to ensure smooth laminar flow into the engine and wing otherwise Bad Things happen. The orange thing that can be seen appears to be the kevlar shroud, and it seems to have done its job: the fan blade didn't come through the side, but instead was ejected out the front and took the cowling with it.
This pilot on youtube has a good take on what happened.
It also turns out that Pratt & Whitney have had trouble with fan blades cracking on these engines before, including one rather similar engine failure in 2018. Oh... and a slightly different 4000 series P&W engine broke on a 747 in Europe over the weekend, too. Suggests an issue with fatigue cracking, so maintenance?
Perhaps they should consider renaming themselves Prat & Twitney?