Respuesta :
Much of humor is contrived by sarcasm, and a sarcastic tone of voice is not easily heard through solely visual mediums. Hope this helped.
Answer:
when people are joking, you could usually tell, because there voice changes, or they are smiling. but in an email you cat really tell either of those things because your reading it. now, some people will text emoticons like XD or :P or say lol if they are joking.