Remnants of the Dual
Although in nearly all words the dual has completely disappeared, it has remained in 2 specific situations. In these 2 situations the dual only remains in the nominative, vocative, accusative, and locative cases. In the dative, genitive, ablative, and instrumental cases the plural takes over the remaining dual usages. With regards to determiner and verb agreement, dual nouns are treated like plural nouns.
1. Body Parts
4 body parts use the dual to refer to those parts when occurring in a complete pair, most notably in humans. For instance while a human's 2 eyes would take the dual form, 2 spider eyes would take the plural as they have more than 2 total. Here are the body parts with dual forms and their declensions
Οψ- Eye (Regular Second Declension Noun)
Ἑς- Hand (Regular Second Declension Noun)
Бοⲝ- Foot (Irregular Third Declension Noun)
Ȏς- Ear (Irregular Third Declension Noun)
2. Counting Days
When counting days (such as "the second day of the festival") or for days of the month (such as April 3rd), Ayôs is used in the singular to refer to the first day and in the dual (Ayi) to refer to the second day. For days above 2 simply the cardinal number is used. Because of this, Kyüweng calendars almost always replace 1 and 2 with Ayôs and Ayi. If there is an exact time on the day in question and it takes place at night (such as "Friday night on May 2nd") then Ayôs/Ayi are replaced with Nops/Nokwi. As Ayôs and Nops typically mean today and tonight respectively in the locative singular, when used for dates they are usually followed by what it's the first date of, such as the month in question.
Αιȏς- Day (Irregular Third Declension Noun)
Nοψ- Night (Irregular Third Declension Noun)