In the détaché stroke we bow along a plane.
When we play sautillé we cut across that plane, the down-bow stroke goes below this plane and the up-bow bounces back up.
To help develop this reaction in the up-bow, it is good to give the bow something to bounce off - a soft leg is ideal.
In order to demonstrate this point Fintan sits with the violin held lower down than usual against his chest, so that the bowscrew hits the leg. The bowhair remains in contact with the string in both strokes....
