Fire making and pneumatic tube: what they have in common

1. Step 1. Fire making — evolved into — Match. A convenient way to make fire.
2. Step 2. Match — uses — Chemical reaction. The head flares up from a chemical reaction set off by friction.
3. Step 3. Chemical reaction — is used in — Capsule. The shell dissolves in the stomach.
4. Step 4. Capsule — is part of — Pneumatic tube. A container for letters.

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