hi,
I think that we can mesure the angle of the bb_bands_High and bb_bands_Low.

I will have two signals:
1) BB is opening the mouth (The price is walking, non-lateral market)
if the angle of bb_bands_high is > 45º
and the angle of bb_bands_low > 45º
the bb is opening the mouth...
(see graph)

2) Check is the price is falling or growing up (buy and sell signal)