Rule 3 : Some nouns have the same form whether singular or plural e.g. Sheep / Deer / Service / Series / Series / Species /Fish / Apparatus.
Ex- I saw two sheep in the zoo.
There are many fish in the pond.

Rule 4 : Few nouns are always used in the plural form only e.g. Cattle / People / Police / Electorate / Poultry / Trousers / Scissors / Spectacles / Binoculars / Crackers / Swine / Gentry / Clergy. All these are used with plural form of verbs.
Ex- The scissors are very sharp.
I need your Binoculars for upcoming trip.