What is happening is that you are straying into the world of countable vs uncountable nouns.
Countable nouns are nouns that are considered in units, eg ducks, chairs, spoons. They come in singular and plural forms.
Uncountable nouns are nouns that are considered in terms of their "mass" for want of a better word, and these are referred to in terms like not much, too much, a bit, a pinch, a drop, etc. Water is a good example of an uncountable noun.
Many nouns are countable and uncountable, and the meaning shifts ever so slightly between them- an excellent example is coffee.
"I feel sick, I drank too much coffee" is correct, as is "waiter, can we order 3 coffees". Slightly different meaning for both.
Lets look at animal/animals. Which of your two examples are correct? Well it depends entirely on the context of the sentence and the meaning the speaker is trying to parley into the sentence.
The 2nd sentence treats the noun animal as a countable noun, giving it a plural form. This gives me an image of someone nibbling in individual animals until they find their favourite. It is a rather cute image, grammatically correct certainly, but slightly comedic in the impression it leaves.
The 1st sentence treats animal as an uncountable noun. This means that you are considering the mass of animals as a single unit. It is a more nuetral sentence.
Toying with countable/uncountable nouns to give a noun more substance or presence or just make it more important is a linguistic trick fashion marketeers have been using for years, the singular pant, shoe, sandal, and so forth.