Okies there is one more for the TIMTOWTDI and the golf fans.
This is probably bad style but see yourself.

#!/usr/bin/perl -w
print ("Enter the word to search >> ");
chomp ($word = <STDIN>);
{
  local $/=undef;
  print grep { $_ =~ $word } <DATA> =~ m!(<MS_\d+>.*?</MS_\d+>)!gs;
}
__DATA__
<MS_1>
  <loc>c:\data\cat.xml</loc>
  <words>dog, cat, fish, bird</words>
</MS_1>
<MS_2>
  <loc>c:\data\cow.xml</loc>
  <words>dog, cat, fish, bird, cow, goat</words>
</MS_2>
<MS_3>
  <loc>c:\data\snake.xml</loc>
  <words>dog, cat, fish, bird, snake, orange</words>
</MS_3>
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