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5.5.6 Concrete non-count nouns

More generally, many concrete nouns that are normally non-count can be treated as count nouns in two uses:

5.5.6.1 When the noun referes to different kins or qualities (sparkling wineS, Italian cheesES)
5.5.62 When the noun refers to quantities in a situation where the units are obvious (ONE sugar, TWO coffeeS)

5.7.1
Some nouns ending in [-th] have the regular plural in spelling, but the pronunciation of [th] is voiced /ð/ and therefore followed by /z/. However, in most cases, the regular pronunciation /θs/ is a variant.

A change of voicing also occurs from the voiceless /s/ ending in singular house to the voiced ending in /zɪz/ in plural [houses].

5.7.2 Mutations

Children... A similar combination appears in brethren, a specialised plural of brother. The older plural ending is found without vowel change in ox/ oxen. In American English there are also variant plurals of ox: regular oxes and  the unchanged form ox. 

5.7.5 Uninflected plurals, without singulars
cattle, livestock, people(as plural of person)
police, poultry, vermin 

5.7.6 Bilnary plurals
binoculars, cloppers, spectacles, briefs

5.7.7 Inflected plurals, without singulars
arms ('weapons')
clothes('garments')
customs('tax')
manners('behaviour')
premises('building')

5.7.9
A few compounds ending in -ful usually take the plural inflection on the last element, but have a less common plural with the inflection on the first element:

mouthful/mouthfuls or mouthsful
spoonful/spoonfuls or spoonsful

5.9.4 Gender: she referring to inanimates
The personal pronoun she may be used to refer to countries and also (though occasionally he occurs) to inanmate entities such as ships, cars and planes.