PROSERO - (prose about Prospero)

You taught me language; and my profit on't
Is, I know how to curse. The red plague rid you
For learning me your language!
frown

— Caliban is denouncing Prospero for teaching ("learning") him his language, declaring that the only good Prospero's language has done him is enabling him to curse; Caliban gives an immediate example of his cursing ability by calling upon the red plague to destroy Prospero for teaching him his language.