Learn Hardcore Russian: Ежевика быстро пачкает пальцы, поэтому дочка ест её очень аккуратно. - Blackberries stain the fingers quickly, so my daughter eats them very carefully.

Breakdown of Ежевика быстро пачкает пальцы, поэтому дочка ест её очень аккуратно.

Why is ежевика singular, when English often says blackberries in the plural?

In Russian, ежевика is commonly treated as a singular mass noun, like blackberry as a general substance or kind of fruit.

So:

Ежевика быстро пачкает пальцы = Blackberries stain your fingers quickly / Blackberry juice stains fingers quickly

Even though English often prefers the plural, Russian often uses the singular here to talk about the fruit in general.

That is also why later the sentence uses её (it) rather than их (them).

Why is it пачкает, not пачкают?

Because the subject is ежевика, which is grammatically singular.

If the subject were plural, for example ягоды (berries), then you would use a plural verb:

What case is пальцы, and why does it look the same as the dictionary form?

Пальцы here is in the accusative plural, because it is the direct object of пачкает.

The dictionary form is nominative plural: