Stirrup tread and payment card: what they have in common

1. Step 1. Stirrup tread — is part of — Stirrup. A foot rest.
2. Step 2. Stirrup — evolved from — Saddle. The stirrup added a foot support to the saddle.
3. Step 3. Saddle — is made of — Leather. A saddle is made of leather.
4. Step 4. Leather — is material for — Wallet. Leather.
5. Step 5. Wallet — uses — Paper money. It holds money.
6. Step 6. Paper money — evolved into — Payment card. The next form of money.

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