Welcome,
Couple of things that may help. Here is the description of how the optional exclusions work:
optionalExclusions can either be set to nil, or given an NSArray of NSStrings which contain phonemes which you do not want to have added to the rejection model. A case in which you might want to do this is when you have over-active rejection such that words that are really in the vocabulary are being rejected. You can first turn on deliverRejectedSpeechInHypotheses: in order to see which phonemes are being detected overzealously and then you can add them to the exclusionArray. Set this parameter to nil if you aren’t using it.
So issue one is that you have to give it phonemes instead of letters, but issue two is that you only use it if you already have a set of phonemes that you’ve verified are being rejected overzealously via the use of the deliverRejectedSpeechInHypotheses setting. It isn’t something you want to start out with.
You haven’t mentioned whether MEOW and MOO are being recognized when they are being said correctly, so let’s start there and then see if I can think of some suggestions for refining things.