Edmund clearly
does care about Charles getting lost, since he’s terrified of being alone in the wood. When he mentions “a bull,” Charles is alluding to the legend of Theseus, who, with the help of a thread, was able to find his way through a vast labyrinth and kill the Minotaur, a half-human, half-bull creature. The allusion suggests that Charles himself is imprisoned in a psychological labyrinth that Edmund has created.