Text: At once a voice arose among     The bleak twigs overheadIn a full-hearted evensong     Of joy illimited;An aged thrush, frail, gaunt, and small     In blast-beruffled plume,Had chosen thus to fling his soul     Upon the growing gloom.
Entailment: A joyful song was sung by a thrush to displace the gloom.
Contradiction: The thrush was so encased in his gloom that he couldn't bare to make a sound.