The first apparition is a severed head with a helmet that, according to the witches, is able to hear Macbeth’s thoughts. This apparition tells him to “Beware Macduff” (4.1.73) and symbolizes Macbeth’s inner thoughts, hence its ability to read his mine unlike the others. This apparition encourages Macbeth to kill Macduff by saying that he is threat to him. The fact that it is a head without a body symbolizes the disconnect between Macbeth’s logic and his conscious - the head being his logic and the body being his conscious because it holds his heart and is absent.
The second apparition is a bloody child who tells Macbeth that no one that was birthed by a woman can harm him which