The Greeks loved metaphor. They loved to compare human emotions and human tendencies with the actions or traits exhibited by animals.
And, because dogs were ever at hand for purposes of comparison, the ways of the dog served as convenient and well-understood metaphor.
Thus they took the word sarkazo and gave it a figurative meaning. Literally it meant “to tear flesh” after the manner of dogs, to snap and rip.
The physical effect upon the animal or person thus attacked by a fierce dog was so similar to the mental effect resulting from a sharp and stinging taunt or gibe that sarkazo seemed perfectly fitted to the latter meaning also.
The caustic remark became sarkasmos.
Altered by Latin sareasmus, this ultimately became English sarcasm.