When stepped on lets little black rods out.
Granted it does not look very nice but still does the job.
Step 1: Shape
Preferebly a circle but any shape u want is good.
Step 2: Mechanism
You know what it means.
Step 3: Just Wait for Someone to Step on It
Even though it has 8 shrapnel (the peices that are fired) it may "unleash" 4-5 schrapnel.
Damn that sounds german.