Final answer:
Justice Wargrave used psychological manipulation to drive Vera Claythorne to hang herself in Agatha Christie's novel. He staged the scene with seaweed to make her death appear self-inflicted, but the orderly placement of the chair suggested another presence, confirming Wargrave's involvement.
Step-by-step explanation:
The question seems to be referring to the psychological games and actions taken by the character Justice Wargrave in the mystery novel And Then There Were None by Agatha Christie. Psychological manipulation by Wargrave was used particularly on Vera Claythorne, the last surviving guest on Soldier Island. Wargrave crafted the situation on the island and the deaths to appear as suic*des or accidents. This induced paranoia, fear, and guilt among the guests.
At the end, after believing she was the last person alive and encountering a setting that Wargrave had designed to play on her guilt and past trauma, Vera ultimately hanged herself. The mention of seaweed relates to a staged scene, which Wargrave used as psychological torture to push Vera to her eventual demise. He intended for it to look like she stood on a chair to hang herself and then kicked it away, but the chair wasn't found kicked over; it was neatly put back against the wall, indicating that someone else, namely Wargrave, had been there after her death to finalize the scene.
Your question is incomplete, but most probably your full question was
That it was Vera Claythorne. That she shot Lombard, took the revolver back to the house, toppled the marble block onto Blore and then - hanged herself. "And that's quite all right - up to a point. There's a chair in her bedroom and on the seat of it there are marks of seaweed same as on her shoes. Looks as though she stood on the chair, adjusted the rope round her neck and kicked away the chair. "But that chair wasn't found kicked over. It was, like, all the other chairs, neatly put back against the wall. That was done after Vera Claythorne's death - by some one else.
How did he use psychological manipulation and seaweed in the end with Vera? Why was she last?