abstract, ache, aggressive, arid, background, biology, cacti, cactus, caution, concept, defense, desert, dry, emotion, feeling, feisty, flora, heat, hook, hurt, keep, macro, nature, needles, off, pain, pierce, pierced, plant, prickly, razor, restricted, restriction, self, sensation, sharp, spike, spikes, spiky, spine, spiny, sting, texture, thorn, thorns, warning