In the Recognising your Opponents Moves course under the "strategy" category (by IM Igor Khmelnitshy & Chess.com staff) what is Black threatening with his move in lesson 1?

(I saw the tactical opportunity for white)

Thanks

Jason

Could you post the position?

yes, here it is below: (Black's last move was Re5-e3.  What was the idea behind this move?  Thanks.

I don't think he threatens anything more complicated than Rxb3. The point of the position being the tactics White has. 

Yes,  beyond the threat  of winning that pawn, black's move (assuming he actually calculated the lines through) ALSO factors in the forcing line Rf8+ followed by RxN removing the guard for the rook on e3.   Still one needs to calculate this till quiescence (no more forcing moves left in the line you are analyzing) and make sure that Black could have safely played this move.  

If I was white, I wouldn't automatically assume "black" made a mistake and rush into Rf8, RxN until I was sure there was no "in-between" move for Black.  

Looking at it, I think this was a blunder.

tactics was the main object of the exercise, it was just that the text said White should also be aware of Black's plan after the Rook move (without hinting at what it might be).

Clearly, whatever it was, it becomes unhinged after 1. Rxf8+ and the moves that follow