Cov kav dej yog cov khoom siv tseem ceeb hauv tsev kom ntseeg tau tias kev siv dej hauv tsev. Hauv lub neej txhua hnub, muaj ntau yam kev siv tsis raug lossis kev saib xyuas yuam kev, uas ua rau muaj teeb meem ntau yam hauv peb cov kav dej. Cov yeeb nkab thaiv dej yog qhov teeb meem ntau tshaj plaws. Yog li ntawd, kev ntsuas los tiv thaiv cov yeeb nkab dej thaiv tau zoo dua tiv thaiv qhov teeb meem ntawm cov yeeb nkab dej thaiv. Qhov teeb meem feem ntau yog qhov ntws tawm los ntawm cov khoom txawv teb chaws. Vim tias tsis muaj cov lim ntsia ntawm cov kav dej, thaum muaj cov khoom txawv teb chaws lossis cov khoom loj tawm ua ke, cov kav dej yuav raug thaiv, uas yog ib qho teeb meem feem ntau ntawm cov yeeb nkab dej thaiv.
