def shuffle_sublists(sublists, rand):
    """
    Shuffles the lists within a list but not the list itself.

    >>> from nutsflow.common import StableRandom
    >>> rand = StableRandom(0)

    >>> sublists = [[1, 2, 3], [4, 5, 6, 7]]
    >>> shuffle_sublists(sublists, rand)
    >>> sublists
    [[1, 3, 2], [4, 5, 7, 6]]

    :param sublists: A list containing lists
    :param Random rand: A random number generator.
    """
    for sublist in sublists:
        rand.shuffle(sublist)
