After saying the blessing over fire during Havdala, we do something (customs vary) involving looking at our fingers by the light of the Havdala candle. I'm wondering how seriously we take this part of the ritual. In particular:
If the person making Havdala doesn't do this, is the fire blessing or the Havdala invalidated?
If the people discharging their obligation by observing the Havdala don't do this, do they lose credit for this blessing of for the Havdala?
How certain must the finger-looker be that the light involved is from the Havdala candle? If most of the light cast on the fingers is from electric lights, does that invalidate the finger-looking?