Subtraction using fingers

Abi counted ten apples on her fingers unprompted. Priscilla decided to try doing subtraction.

If I eat one apple, how many are left?

Abi put down one of her ten outstretched fingers and counted nine.

This process was repeated smoothly until zero was reached.

When Priscilla tried to eat 2 of 7 apples she was reminded that the sequence was only one at a time.