The Crow and Mercury_英语寓言故事

a crow caught in a snare prayed to apollo to release him, making
a vow to offer some frankincense at his shrine.
but when rescued
from his danger, he forgot his promise.
shortly afterwards,
again caught in a snare, he passed by apollo and made the same
promise to offer frankincense to mercury.
mercury soon appeared
and said to him, "o thou most base fellow? how can i believe
thee, who hast disowned and wronged thy former patron?'