  We consider the emergent tetrad gravity and the analog of antispacetime
realized in the recent experiments ( J.T. Makinen, et al., Nat. Comm. 10, 237
(2019)) on the composite defects in superfluid $^3$He: the Kibble walls bounded
by strings (the half quantum vortices). The antispacetime can be reached in two
different ways: by the "safe" route around the Alice string or by dangerous
route across the Kibble wall. This consideration also suggests the scenario of
the formation of the discrete symmetry -- the parity $P$ in Dirac equations --
from the continuous symmetry existing on the more fundamental level.
