# this code creates an endless loop
my %hash = (
  foo=>"x",
  Foo=>"y",
  Bar=>"a",
  bar=>"c"
);
while(my($key,$value)=each %hash){
   # dumb example 
   for my $key2 (keys %hash){
       if(lc($key) eq lc($key2)){
         print "key $key is similiar to $key2\n";
       }
   }
}