Using mypy 0.761, Python 3.7.5 here. The ANIMALS2 value is highlighted as incorrect by Mypy:

COW: Literal['cow'] = 'cow'
PIG: Literal['pig'] = 'pig'
ANIMALS1: Literal['cow', 'pig']  # This is OK
ANIMALS2: Literal[COW, PIG]
#         ^^^^^^^ Mypy: Parameter 1 of Literal[...] is invalid

But it seems Mypy should be able to deduce that ANIMALS1 and ANIMALS2 are the same thing?

I'm not sure if the more lax version should be allowed as well, but seems useful:

OX = 'ox'
ANIMALS = Literal[OX]