Sentence Completion

Complete the sentence with ONE word from the passage for each blank.

The hagfish, a primitive eel-shaped marine animal, defends itself in an unusual way. When threatened, it releases a tiny amount of a special substance that instantly expands into a thick cloud of slime by absorbing surrounding seawater. This gel clogs the gills of attacking predators, forcing them to retreat. A single hagfish can produce enough slime to fill a bucket in seconds. Engineers now study the material because its fibres are remarkably strong yet form from almost nothing.

The hagfish protects itself by producing a cloud of that blocks a predator's .