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$_ = <<SENTENCE;
There once was a doggy in the window. I went into the store 
and inquired about the price, the doggy was too nice to ever 
think twice, so now I have a doggy to care for.
SENTENCE

my @vowels = ( /[aeiuo]/gi );

my @vowels = ( /[aeiou]|y(?![aeiou])/gi );

my @vowels = ( /[aeiou]|(?<![aeiou])y(?![aeiou])/gi );