Shakespeare has chosen to use a “poisoned sword” and the “poisoned chalice” to end the lives of the main characters in the play.why is this symbolic in the play?

Since this is not my area of expertise, I searched Google under the key words "Shakespeare poison symbol" to get these possible sources:

http://summarycentral.tripod.com/romeoandjuliet.htm
http://education.yahoo.com/homework_help/cliffsnotes/romeo_and_juliet/79.html

I hope this helps. Thanks for asking.