A definition article on everything2.com (May 14, 2000): arfle barfle gloop? Response of the long-dead Level 9 software company's parser in Snowball (the ancient adventure game on the BBC micro, one of the greatest ever written) to any sentence (more properly, utterance) that it didn't understand. Might be loosely translated as "what the hell was that supposed to be?". And much more fun than SYNTAX ERROR.