Both Laertes and Gertrude, after they are slain, can be seen breathing visibly.
Laertes, wanting to avenge his father's and sister's death, conspires with Claudius to kill Hamlet. For this purpose, a cup of wine is poisoned and the sword drained in poison. However, when he sees that Hamlet tries to drink from the poisoned cup, instead of letting him do so, he deters him by cutting Hamlet with his poisoned sword.