  Recent experimental realizations of superfluid mixtures of Bose and Fermi
quantum gases provide a unique platform for exploring diverse superfluid
phenomena. We study dipole oscillations of a double superfluid in a
cigar-shaped optical dipole trap, consisting of $^{41}$K and $^{6}$Li atoms
with a large mass imbalance, where the oscillations of the bosonic and
fermionic components are coupled via the Bose-Fermi interaction. In our
high-precision measurements, the frequencies of both components are observed to
be shifted from the single-species ones, and exhibit unusual features. The
frequency shifts of the $^{41}$K component are upward (downward) in the radial
(axial) direction, whereas the $^{6}$Li component has down-shifted frequencies
in both directions. Most strikingly, as the interaction strength is varied, the
frequency shifts display a resonant-like behavior in both directions, for both
species, and around a similar location at the BCS side of fermionic superfluid.
These rich phenomena challenge theoretical understanding of superfluids.
