Facehugger

Acidic Blood 1
{1}{b}{b} Facehugger loses this ability and becomes
an Aura; it is still a creature. Enchant target
creature, it can't attack or block, and its activated abilities can't be activated.
If enchanted creature is a human, destroy it and Facehugger, then search your library for a card
named 'Chest Burster' and put it onto the battlefield tapped. Shuffle your library.