Either he's afraid because he's been up to some pranks himself...

or he's not afraid for himself, but is simply egging me on to give them all away! Ach, it's terrible, Lebyadkin! Ach, you must not make a blunder!" He was so absorbed in thought that he forgot to listen.

It was not easy to hear either.

The door was a solid one, and they were talking in a very low voice.

Nothing reached the captain but indistinct sounds.