verb

speak rapidly and unintelligibly, typically through fear or shock.

they shrieked and gibbered as flames surrounded them

prattle,rattle on,chatter,babble,ramble,drivel,jabber,patter,gabble,bumble,burble,twitter,go on,run on,mutter,mumble,maunder,prate,bleat,cackle,slabber,gab,yak,yap,yackety-yak,yabber,yatter,natter,yammer,blabber,jibber-jabber,blather,blether,blither,jaw,gas,shoot one’s mouth off,witter,rabbit,chunter,waffle,flannel,run off at the mouth,mag,clack,twaddle,twattle