Now consider six blue socks, all the same length. Some are fluffy, and some are smooth.

Six blue socks, all the same length: some fluffy, some smooth.

Color can't sort them: every sock is blue. Length can't sort them: every sock is the same length.

How they feel can sort them: the fluffy socks together, the smooth socks together.

Sorted by how they feel: fluffy socks in one group, smooth socks in the other.

Now consider six green leaves, all the same size. Some are pointed, and some are round.

Six green leaves, all the same size: some pointed, some round.

Color can't sort them, and size can't. Shape can: the pointed leaves together, the round leaves together.

Sorted by shape: pointed leaves in one group, round leaves in the other.