Just to expand a little on what Tanktalus said... instead of creating a regular expression with the qr// quote, you just created a normal string that happened to contain a perl expression.
my $word = "Apple";
my $pattern_quoted = "qr/^(Orange|Apple|Grape|Halibut)$/i";
print "Pattern matched\n" if ($word =~ m/$pattern_quoted/);
print "Eval'd pattern matched\n" if ($word =~ eval($pattern_quoted));