Mark 9:6

6(He did not know what to say, they were so frightened.)

6For he did not know how to reply; for they became terrified.

6For he did not know what to answer; for they became terrified.

6For he did not [really] know what to say because they were terrified [and stunned by the miraculous sight].

6For they were all so terrified that Peter did not know what else to say.

6Peter didn’t really know what to say, because they were so afraid.