Coral snakes in the United States are red, black, and yellow. The Florida Museum of Natural History describes the harlequin (eastern) coral snake as a thin-bodied snake with broad red and black rings separated by narrow yellow rings, a rounded black snout, and a broad yellow band behind the eyes. The red rings often carry black flecks, and the tail has only black and yellow bands.
On a coral snake, the red rings touch the yellow rings. Harmless look-alikes in Florida, such as the scarlet kingsnake and scarletsnake, have red snouts and yellow rings that touch only black. The museum notes that rhymes like “red touches yellow, kill a fellow” hold true most of the time in Florida, but unusual color variations occur, so any snake you cannot identify with certainty is best left alone.
Source: Florida Museum of Natural History, Florida Snake ID Guide: Harlequin Coralsnake
Image: Eastern coral snake (Micrurus fulvius), Jacksonville, Florida, Norman.benton, CC BY-SA 3.0, via Wikimedia Commons.