“Expression consists for us in incalculability. If I knew exactly how he would grimace, move, then there would be no facial expression, no gesture.”
There is a sense in which a grimace or wink (for example) are part of a code of expression – so, for instance, they are commonly understood, and can be represented iconically. They are in this sense 'calculable'. But a smile or wink that simply conformed to the accepted code would be expressionless (mechanical). It is a condition of expression that some ‘disturbance’ of this code must take place. This disturbance of the code (by affect) is part of what is meant by individual expression. But there cannot of course be disturbance without the code.
Once again expression requires predefined shapes but only in order to surpass them. Expression lives in the disturbance not the code.