def fuse_scribbles(scribbles_a, scribbles_b):
    """ Fuse two scribbles in the default format.

    # Arguments
        scribbles_a: Dictionary. Default representation of scribbles A.
        scribbles_b: Dictionary. Default representation of scribbles B.

    # Returns
        dict: Returns a dictionary with scribbles A and B fused.
    """
    if scribbles_a['sequence'] != scribbles_b['sequence']:
        raise ValueError('Scribbles to fuse are not from the same sequence')
    if len(scribbles_a['scribbles']) != len(scribbles_b['scribbles']):
        raise ValueError('Scribbles does not have the same number of frames')
    scribbles = dict(scribbles_a)
    nb_frames = len(scribbles['scribbles'])
    for i in range(nb_frames):
        scribbles['scribbles'][i] += scribbles_b['scribbles'][i]
    return scribbles
