The cottonmouth will generally curl into a strike position and gape open its jaws, thereby showing the reason they are called cottonmouths. The two large fangs that are hinged back when the snake closes its mouth are sometimes visible as well. If you are close enough to note the fangs, then you are way too close.
A eunuch is a castrated human male. The castration can be only of the testes, or also include the penis, known as a penectomy (often with a tube inserted to keep the urethra open, called a urethral rerouting). The practice was established before 700 BC and accounts of eunuchs are known throughout history.
If you vouch for someone, you provide evidence or guarantee something on their behalf. If you vouch for your brother, you're saying he's a stand-up type of guy. First used in the 14th century, vouch comes from the Latin vocitare, (to call, call upon, or summon). Sometimes it can mean offering supporting evidence, as when, for example, you're summoned to court to testify on someone's behalf. If you write a letter of recommendation for a student or co-worker, you vouch for their character and abilities.