Alrighty then, here goes. Works best with contrast colours. And a smaller hook.
Step 1. Prepare to be amazed.
Step 2: Insert hook into inner loop of top square.
Step 3. Insert hook into inner loop of bottom square.
Step 4. Loop yarn over hook.
Step 5. Pull yarn through all three stitches on hook.
Step 6. Admire the handiness.
Aerial view of finished hook: