Birthing Pod, an artifact from New Phyrexia, has an activated ability that allows you to search your library for creature cards. This ability has an additional cost of sacrificing a creature you control. The creature card you end up finding must have a converted mana cost equal to one plus the converted mana cost of the sacrificed creature.
Sacrificing this creature is an additional cost to activate this ability. As it is a cost, it cannot be responded to. A player cannot respond to this ability by playing a spell or ability in an attempt to remove the sacrificed creature from play to prevent the ability from being activated. Once this player has priority during one of the main phases of his turn, he can activate this ability.
Immediately after a spell or ability resolves, the active player will receive priority. This means that after the player casts and resolves a creature in one of the main phases of his turn, he will receive priority again. This player can then choose to activate the Birthing Pod ability and sacrifice the creature that just entered play.