Perhaps as a relic of an ancient Roman custom of planting parsley on graves, a sprig of parsley was either associated with the devil or as an antidote for poison. Adding a sprig to a plate of food may have originated as a gesture of good faith and as way to safeguard the meal from evil.

People are lot less judgy when you say you ate an 'avocado salad' instead of a bowl of guacamole.