```ts
export function flipOne(pair: string[]): string[] {
  if (pair.length !== 2) throw new Error("Pair must have exactly two members");
  return [pair[1], pair[0]];
}

export function flipAll(pairs: string[][]): string[][] {
  for (let i = 0; i < pairs.length; i++) {
    pairs[i] = flipOne(pairs[i]);
  }
  return pairs;
}
```