If You Play with a Living Anemone with a Probe,it

If you play with a living anemone with a probe,it will withdraw even if you vibrate the probe like a food animal would vibrate; it also withdraws if you just add sugar.However,it reaches out and grasps an object that both vibrates and tastes like food.The use of such a double system prevents unnecessary firing of expensive nematocysts.Why are nematocysts "expensive"?

A) The organism dies without nematocysts.
B) The research equipment to detect them is very expensive.
C) Nematocysts are used in medicine and are very expensive to harvest.
D) The nematocyst is very complex and costs the anemone much energy to build.
E) The nematocyst can only be used for food and doesn't "fire" for non-food objects.