▁st om ach . ▁The ▁fur ▁becomes ▁dens er ▁and ▁th icker ▁from ▁fall ▁through ▁the ▁winter . ▁The ▁sh rew ▁usually ▁has ▁ 3 0 ▁teeth , ▁but ▁the ▁ 4 th ▁upper ▁intermediate ▁to oth ▁is ▁very ▁small ▁( r ud iment ary ), ▁and ▁is ▁absent ▁in ▁some ▁individuals . ▁Near ▁the ▁mouth ▁grow ▁a ▁dense ▁array ▁of ▁short ▁wh isk ers , ▁which ▁the ▁sh rew ▁act ively ▁uses ▁to ▁search ▁for ▁pre y , ▁especially ▁in ▁the ▁night . ▁Dim orphism ▁in ▁body ▁features ▁between ▁males ▁and ▁females ▁is ▁absent . ▁ ▁Activity ▁E tr us can ▁sh rew s ▁live ▁alone , ▁except ▁during ▁m ating ▁periods . ▁Their ▁lif es pan ▁is ▁estimated ▁at ▁typically ▁around ▁two ▁years , ▁but ▁with ▁a ▁large ▁uncertainty . ▁They ▁protect ▁their ▁territ ories ▁by ▁making ▁ch ir ping ▁no ises ▁and ▁signs ▁of ▁ag gress iveness . ▁They ▁tend ▁to ▁gro om ▁themselves ▁constantly ▁when ▁not ▁e ating , ▁and ▁are ▁always ▁moving ▁when ▁aw ake ▁and ▁not ▁hiding . ▁The ▁hiding ▁periods ▁are ▁short , ▁and ▁typically ▁last ▁less ▁than ▁half ▁an ▁hour . ▁Click ing ▁sounds ▁are ▁heard ▁when ▁these ▁sh rew s ▁are ▁moving , ▁which ▁ce ase ▁when ▁they ▁rest . ▁The ▁sh rew s ▁are ▁more ▁active ▁during ▁the ▁night ▁when ▁they ▁make ▁long ▁tri ps ; ▁during ▁the ▁day , ▁they ▁stay ▁near ▁the ▁nest ▁or ▁in ▁a ▁hiding ▁place . ▁They ▁reach ▁their ▁maximum ▁level ▁of ▁activity ▁at ▁dawn . ▁ ▁The