Why do sisters curse their brothers 'You die' & prick tongues with thorn in Bihar on Bhai Dooj?

In Bihar's Mithila region, sisters first symbolically curse their brothers, "You die," so that their future troubles are averted. After this, they perform a puja and atone by piercing their tongues with thorns from a rengni (thorn bush). This ritual is considered a symbol of the brother's longevity, happiness, and prosperity. Pricking tongues symbolically signifies sisters' sacrifice.