Rocking horse and sewage treatment plant: what they have in common

1. Step 1. Rocking horse — uses — Pendulum. Rocking.
2. Step 2. Pendulum — is used in — Tuned mass damper. A pendulum.
3. Step 3. Tuned mass damper — is made of — Concrete. Or concrete.
4. Step 4. Concrete — is material for — Sewage treatment plant. The tanks are concrete.

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