Nouns used in a particular sense
Many of the nouns in the above groups can be used in a particular sense and are then countable and can take a/an in the singular.
Some examples are given below:
hair(all the hair on one's head) is considered uncountable, but if we consider each hair separately we say one hair, two hairs etc.:
Her hair is black (uncountable noun).
Whenever she finds a grey hair she pulls it out (countable noun)
We drink beer, coffee, gin, but we can ask for a (cup of) coffee, a gin, two gins etc. We drink out of glasses. We can walk in woods.
These, with hair, information, knowledge, news, rubbish, are sometimes countable in other languages.