Answer

Metaphors are used to describe the frogs and ‘their blunt heads farting’ which is a gross, unpleasant image, making the sound of a fart link to the noise the croaking frogs make, which makes it seem natural but unpleasant and disgusting (also linking to the rotten smell).

Personification ‘great slime kings’ describes the frogs as if they are the most powerful slimy things you could imagine, superior to all other things and they are gathered ‘for vengeance’ so there is a huge sense of threat that they will do immense damage.