  We address the origins of the quasi-periodic breathing observed in [Phys.
Rev.\ X vol. 9, 021035 (2019)] in disk-shaped harmonically trapped
two-dimensional Bose condensates, where the quasi-period
$T_{\text{quasi-breathing}}\sim$~$2T/7$ and $T$ is the period of the harmonic
trap. We show that, due to an unexplained coincidence, the first instance of
the collapse of the hydrodynamic description, at $t^{*} =
\arctan(\sqrt{2})/(2\pi) T \approx T/7$, emerges as a `skillful impostor' of
the quasi-breathing half-period $T_{\text{quasi-breathing}}/2$. At the time
$t^{*}$, the velocity field almost vanishes, supporting the requisite
time-reversal invariance. We find that this phenomenon persists for
scale-invariant gases in all spatial dimensions, being exact in one dimension
and, likely, approximate in all others. In $d$ dimensions, the quasi-breathing
half-period assumes the form $T_{\text{quasi-breathing}}/2 \equiv t^{*} =
\arctan(\sqrt{d})/(2\pi) T$. Remaining unresolved is the origin of the
period-$2T$ breathing, reported in the same experiment.
