Fumulus, the Infestation

If a nontoken creature is sacrificed to pay a cost of a spell or ability, Fumulus's thirdsecond ability will resolve before that spell or ability. Conversely, if a nontoken creature is sacrificed during the resolution of a spell or ability, that spell or ability will finish resolving before Fumulus's second ability is put onto the stack.

If you sacrifice Fumulus, its thirdsecond ability will still trigger.