Ducky & Littlefoot practiced the earlier statement till they go it right. Then hearing Chomper give them a new phrase and they practiced it.
Ducky went slow and got most of it correct or close, getting better at speaking sharptooth. The first attempt she got, <Hep! The Sharptooth iis chosing os!> she practice more and got closer to the correct pronunciation till she finally got there.
Littlefoot spoke slower as Ducky was doing and got much the same for his first attempt getting, <Hllp! Th sharptooth iis chasssng us!> and with further practice got closer and closer till he got it right.