Cantreestalk?Yes,butnotinwords.Scientistshavereasontobelievethattreesdocommunicatewitheachother.Notlongago,researcherslearnedsomesurprisingthings.Firstawillowtreeattackedinthewoodsbycaterpillars(毛虫)changedthechemistryofitsleavesandmadetheirtastesoterriblethattheygottiredoftheleavesandstoppedeatingthem.Thenevenmoreastonishing,thetreesentoutaspecialsmell----asignal(信号)causingitsneighborstochangethechemistryoftheirownleavesandmakethemlesstasty.Communication,ofcourse,doesn'tneedtobeinwords.Wecantalktoeachotherbysmiling,raisingourshouldersandmovingourhands.Weknowthatbirdsandanimalsuseawholevocabularyofsongs,soundsandmovements.Beesdancetheirsignals,flyingincertainpatternsthattellotherbeeswheretofindnectar(花蜜)forhoney.Sowhyshouldn'ttreeshavewaysofsendingmessage?31.Itcanbeconcludedfromthepassagethatcaterpillarsdonotfeedonleavesthat______.