Oracle Text

Whenever you sacrifice another permanent, put a +1/+1 counter on Bloodbriar.

Card Rulings

7/13/2016 Bloodbriar’s ability doesn’t give you permission to sacrifice permanents. You’ll need another effect that instructs or allows you to sacrifice them.
7/13/2016 If you sacrifice a permanent as part of a spell or activated ability’s cost, Bloodbriar’s ability will resolve before that spell or ability.