the real question... why does (sic) pain and agony exist
They exist because we are biological organisms with nervous systems that evolved to detect pain, in order to allow us to detect threats to our survival so as to escape from them in the present and learn to avoid them in the future.
An even more profound existential question however was put forth in 1956 by Frankie Lymon and the Teenagers, but even that is rather easily answered by evolutionary biology.
Helium II is a superfluid, a quantum mechanical state of matter with strange properties .
The thermal conductivity of helium II is greater than that of any other known substance, a million times that of helium I and hundred of times that of copper. This is because heat conduction occurs via a quantum mechanism.
Second sound is a quantum mechanical phenomenon in which heat transfer occurs by wave-like motion, rather than by the usual mechanism of diffusion. Heat takes the place of pressure in normal sound waves. This leads to very high thermal conductivity. It's known as "second sound" because the wave motion of heat is similar to the propagation of sound in air.
Sound waves are fluctuations in the density of molecules in a substance; second sound waves are fluctuations in the density of phonons. Second sound can be observed in any system in which most phonon-phonon collisions conserve momentum. This occurs in superfluids and in dielectric crystals when Umklapp scattering is small.