  In the electromagnetic multipole expansion, magnetic octupoles are the
subsequent order of magnetic multipoles allowed in centrosymmetric systems,
following the more commonly observed magnetic dipoles. As order parameters in
condensed matter systems, magnetic octupoles have been experimentally elusive.
In particular, the lack of simple external fields that directly couple to them
makes their experimental detection challenging. Here, we demonstrate a
methodology for probing the magnetic octupole susceptibility using a product of
magnetic field $H_i$ and shear strain $\epsilon_{jk}$ to couple to the
octupolar fluctuations, while using an adiabatic elastocaloric effect to probe
the response to this composite effective field. We observe a Curie-Weiss
behavior in the obtained octupolar susceptibility of \ce{PrV2Al20} up to
temperatures approximately forty times the putative octupole ordering
temperature. Our results demonstrate the presence of magnetic octupole
fluctuations in the particular material system, and more broadly highlight how
anisotropic strain can be combined with magnetic fields to formulate a
versatile probe to observe otherwise elusive emergent `hidden' electronic
orders.
