  We recompute the invisible Higgs decay width arising from Higgs-graviscalar
mixing in the ADD model, comparing the original derivation in the non-diagonal
mass basis to that in a diagonal mass basis. The results obtained are identical
(and differ by a factor of 2 from the original calculation) but the
diagonal-basis derivation is pedagogically useful for clarifying the physics of
the invisible width from mixing. We emphasize that both derivations make it
clear that a direct scan in energy for a process such as $WW\to WW$ mediated by
Higgs plus graviscalar intermediate resonances would follow a {\it single}
Breit-Wigner form with total width given by
$\Gamma^{tot}=\Gamma_h^{SM}+\Gamma_{invisible}$. We also compute the additional
contributions to the invisible width due to direct Higgs to graviscalar pair
decays. We find that the invisible width due to the latter is relatively small
unless the Higgs mass is comparable to or larger than the effective
extra-dimensional Planck mass.
