I realize that some perl coders can't seem to get out of bed in the morning without writing 5 map statements. The map is not that gratuitous here. The arrangement of the code though, with the buried uc() and the odd parentheses, is confusing. Here's a somewhat easier to read re-formatting:

return map { split(' ', uc $_, 2) } @somearray;
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I might also break this into two, because the in-line makes the uncommon 3rd arg to split harder to pick up when scanning.

my @separated = map { split(' ', $_, 2) } @somearray;
@separated    = map { uc $_ }             @separated;
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Yes, it's probably slower. I don't care about the odd millisecond if it's easier to read. Some decent variable names would also make a big difference here.