Normally I am under the impression that "au" and "ai" are pronounced like the word "eye," but when "au" is part of a plural form, it is usually pronounced "eh," unless there is an accent over it. "ai" is usually pronounced like "eye" but I have noticed in some words it is pronounced "eh." The plural of llygad meaning eye is llygaid, but instead of being pronounced llygEYED it is pronounced llygED. Are there any rules about these situations? I am particularly puzzled by the llygad / llygaid situation.