Language
Act IV
Lee Slug

IV.vii
"...so mortal that, but dip a knife in it, where it draws blood no cataplasm so rare..."
mortal: deadly
cataplasm: poultice
This section is very crucial for the audience's understanding of the rising action for the climax to come. If the audience doesnt uderstand what Laertes is saying, then  he/she doesnt understand the extensive plot to kill Hamlet.

"...the rather if you could devise it so that I might be the organ."
organ: agent, instrument
Laertes is expressing here that if Claudius can arrange a plan, Laertes would like to be the person that kills Hamlet.

IV.v
"O, this is counter, you false Danish dogs!"
counter: hunting dogs that follow the wrong path