"There's a lot" or "there are a lot"?
I don't know where I got the idea that "there's" is incorrect to introduce a plural, as in "There's a lot of animals here." But somewhere along the line this idea became deeply ingrained. I suppose it's possible I arrived at this conclusion on my own. After all, when you consider the correct sentences "There is a cat outside" and "There are cats outside," it's pretty clear that the noun governs the verb. (This is called a notional subject.)
But when you throw in a modifying term or two, it shifts the focus away from the noun, causing people to stop caring whether it's singular or plural. That is, the modifying phrase "a lot" sounds singular. So people who would never say "There's animals here," instead opting for the plural verb form in "There are animals here," are affected by the interceding "a lot": "There are animals here," but "There's a lot of animals here."
That's why "there's" before a plural is often considered idiomatic -- basically, correct. But to me "There's a lot of animals here" will always sound as wrong as "There is a lot of animals here."