I was told the following story with an Indian boy and rattlesnake growing up, but the principle is just as poetic. From Wikipedia:

The Scorpion and the Frog is a fable of unknown author, often mis-attributed to Aesop. The story is about a scorpion asking a frog to carry him across a river. The frog is afraid of being stung, but the scorpion reassures him that if it stung the frog, the frog would sink and the scorpion would drown as well. The frog then agrees; nevertheless, in mid-river, the scorpion stings him, dooming the two of them. When asked why, the scorpion explains, “I’m a scorpion; it’s my nature.”

In other words, “You knew what I was when you picked me up.”