Reaper and zip: what they have in common

1. Step 1. Reaper — evolved from — Sickle. Mechanical reaping.
2. Step 2. Sickle — uses — Wedge. The cutting edge is a wedge.
3. Step 3. Wedge — is part of — Zip. The slider works like a wedge, bringing the teeth together and pushing them apart.

Open Evothings