Puzzle #170: Critters

Here are two groups of imaginary critters.

Group one consists of the ferocious: reamble, nozgot, jeret, plogleno, ugluckon.

Group two consists of the rather meek: friddert, stardby, enstalbgir, apprin, ytterinkob.

What do the critters in group one have that the critters in group two do not have? (It has to do with their name words.)

Submit your answer to Gene Wirchenko <genew@telus.net>. Your answer should be in the form of a proof. That means to show how your answer must be correct. The deadline is Wednesday, September 7, 2016 at noon Pacific Time. I will post the answer shortly after.