A kind soul has explained in a message that on f6, the knight can capture on h5 which I hadn't seen 
Soviet Chess Primer: PLease explain this
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Jan 15, 2021
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#2
In this one the Nh6? move is commented
"An unsuccessful way to defend the point f7, as the knight on h6 will presently be eliminated by the white bishop on c1. A sound defense would be 3... Nf6"
I don't understand how Nf6 defends anything? The queen can still take the f7 pawn via Qh5, and I don't see how the knight is helpful in that position.