1. Shakespear makes the audience laugh in situations which in real life will cause a great pain.
Eg: The two twins' seperation. In the play we don't feel any pain at all, but in real life it's not funny it's actually causing a huge pain.
2. He added the presence of clown (two Dromios).
3. He added funny foolish characters (two Dromios).
4. The mistaken identities between the characters.