Snape can't stand being called a coward--or not

[literature_Caro]

No: HPFGUIDX 135811

Juli17
>  In this first exchange, Snape doesn't seem that upset, and 
>  there's no expression of rage or pain. He takes no action against
>  Harry but simply insults James, which of course further angers 
>  Harry.

Caro: I would like to suggest that Snape there still can control
himself far enough "just" to insult James Potter and therefore tries
to hurt Harry. Harry has always shown some weakness on that point.
  
Juli17:
>  Then Harry feels a white-hot whiplike something hit him across the
>  face, and is slammed back against the ground. (And is the first, and
>  only, time Snape physically takes action against Harry)

Caro:
What about Buckbeak? He there arrives to defend Harry. Couldn't it be
that Harry was stroked by his wings or tail? I don't think that Snape
really had the time to curse Harry and there was no mentioning of him
of Buckbeak being affected in any way.
  
But apart from these little additions I do agree with you.

Caro