Random distributions exhibit chance clumps (see Poisson clumping). Clumping clay cat litters are natural products. Melic grasses are clumping to short-rhizomatous grasses. Most biodegradable litters last longer than the equivalent size of clay or clumping clay litters. Acrocarps are thick, upright, mounded/clumping in habit, and slower-growing. These agents reduce the aggregation ("clumping") of platelets by irreversibly binding to P2Y receptors. The wax improves moisture resistance and the resin initially helps reduce clumping. This phenomenon is sometimes known as "clumping" or "bunching". Wax prevents fibers from clumping together during storage. It involves the clumping of keratin filaments. It has creeping rhizome (approximately diameter), forming a dense clumping plant. The smear is used to examine platelets for size, shape, qualitative number, and clumping. A negative test shows no clumping of gelatin particles. Amyloid, the aggregation, or clumping, of proteins, is resistant to degradation by the body. Beetles use rock crevices as hibernacula, often clumping in them, in groups.