my $str = "It/PRP really/RB does/VBZ seem/VB to/TO violate/VB a/DT lot/NN of/IN boundaries!/NNS";

my @pairs = map { [ m!(\w+).*?/(\w+)! ] } split /\s+/, $str;

for (0..$#pairs-1) {
    print $pairs[$_][0], " ", $pairs[$_+1][0], "\n";
}