Looks like Tenma was too concerned about her own business (reconciliation with Eri) to pay attentipn to Yakumo's strange actions. As for Sara - you are probably right, she is the one who'll pay attantion to this act and will be worried - but I doubt that she'll ever recognize about this episode. So, in the end, noone will think about Yakumo's action deeply enough to start worrying.
Originally Posted by shimano87
About significance for the progress - I'm not sure. She was offencive to those who somehow went against her sister before too - with Hanai and Eri (at festival). But, since back then harm made to Tenma was not that serious as in slap case, her reaction was softer too. Now she just reacted corresponding to the measure of harm - the harm was bigger so reaction is more serious too. As in earlier cases she (as she probably thought she was) defended her sister from the enemy - which conforms with her character - but, on the other hand, we never got such a powerful reaction - which was not expected (at least by me), so it brings new colours to her character portrait.