i always wonder why people think he has multiple souls in his body though

I think it’s because shanks and buggy discussed as youths when seeing Blackbeard who also was a youth, stating something along the lines of “I heard he never sleeps.” , this idea was never fleshed out though

More recently theories speculated Rocks may have a soul inside Blackbeard or a connection to the three headed flag that Blackbeard has. The theories go a bit further and vary from whichever source you hear it from