This whistle comes from Donald's Off Day, a Donald Duck cartoon released on 8 December 1944, where the bright, high sound fits the cartoon's playful railway and travel humour. Short excerpts like this later circulated as stock cartoon sound effects, valued because a single half-second whistle is instantly recognisable as a train without needing any picture. That clarity is why editors still reach for it today, especially for retro, slapstick and animated projects where a modern, realistic train horn would feel too heavy or serious.