Casiopea said:There's a pair of socks in the drawer.
There's a unit in the drawer.
There's a couple of pairs of socks in the drawer.
There are several units.
They're a pair of thieves.
They're a couple of thieves.
So ther is no explanation for it. We can use this construction as we wish: both there is and there are even if they are followed by a singular or a plural noun.;-)LGSWE:
In fact, such examples [singular '"there's + plural noun phrase] are somewhat more common in conversation than the standard constructions with plural verb plus plural noun phrase.
The special behavior of there's is matched by a similar tendency for here's, where's, and how's:
Here's your shoes.
Where's your tapes.
How's mum and dad.
A: How's things?
B: Not too bad.