Lub luag haujlwm tseem ceeb ntawm cov hniav hauv cov tshuab luam ntawv thiab cov tshuab luam ntawv yog tu. Qhov zoo ntawm cov hniav feem ntau yog nyob ntawm nws cov khoom, uas yuav tsum tiv taus qhov kub thiab txias. Feem ntau hais lus, cov hniav yuav maj mam hnav tom qab ib lub sijhawm thiab yuav tsum tau hloov tsis tu ncua. Yog tias cov hniav hnav hnyav heev, cov hniav yuav tsum tau muab tshem tawm thiab hloov nrog ib qho tshiab.
