"Bears do not bark, but they shout."
Translation:A medvék nem ugatnak, hanem üvöltenek.
"Shout" isn't a great choice of word for the English sentence, because (1) Bears don't "shout" in English (unless they're anthropomorphic storybook bears) - actually I'm pretty sure that "shout" is used only with humans or creatures in stories that are capable of speech. And (2), it's quite difficult for people to guess that üvölt is called for rather than kiabál.
The most typical English word for a noise bears make is "roar", which would also be a better match for üvölt.
Why does üvölt take an "e" before the "nek", whereas ugat doesn't take an extra vowel?
The consonant cluster -ltn- is felt to be too difficult to pronounce, so a vowel is added to make it easier; -tn- on the other hand has only two consonants and is easy enough to pronounce on its own.