What does Holmes replace the pocket in the moat after finding it? ACT 2, SCENE 9-EPILOGUE

Holmes replaced the bundle (weighted down with a dumb-bell), so that whoever had placed it there in the first place would go beck to retrive when it was announced that the moat would be drained.

“It was of the first importance, however, that we should be able to prove who placed it there. This we accomplished by the very obvious device of announcing that the moat would be dried to-morrow, which had, of course, the effect that whoever had hidden the bundle would most certainly withdraw it the moment that darkness enabled him to do so. We have no less than four witnesses as to who it was who took advantage of the opportunity, and so, Mr. Barker, I think the word lies now with you.”