snt --> det(F, Number), adjs(F), noun(Number), verb(Number).
det(F, sing) --> [a], { F = consonant } ;
                 [an], { F = vowel }.
det(_, plur) --> [the].
adjs(F) --> adjs(F, 0).
adjs(F, Count) --> adj(F) ;
                   { Count < 1, NewCount is Count + 1},
                   adj(F), adjs(_, NewCount).
adj(F) --> [spotted], { F = consonant } ;
           [endangered], { F = vowel } ;
           [poison_arrow], { F = consonant }.
noun(Num) --> [frog], { Num = sing } ;
              [owl], { Num = sing } ;
              [frogs], { Num = plur } ;
              [owls], { Num = plur }.

verb(Num) --> [hops], { Num = sing } ;
              [hop], { Num = plur } ;
              [swims], { Num = sing } ;
              [swim], { Num = plur } ;
              [hunts], { Num = sing } ;
              [hunt], { Num = plur } ;
              [flies], { Num = sing } ;
              [fly], { Num = plur }.