Rolls/trips off the tongue
If spoken words roll or trip off the tongue, it means they come easily, and/or are pleasant to say, i.e. the words flow without effort. The origin is obscure. Shakespeare writes about a speech that comes 'trippingly off the tongue' meaning that the words comes lightly or easily (Hamlet Act III, Scene II) which indicates that the concept was around from at least the 1500s. Google N-gram graphs, however, based on the contents of thousands of books from 1800 onwards, point to a date of origin for 'rolls/trips off the tongue' from around the mid-19th century, indicating that these formats came much later than the Shakespearean example.