The dagger that clatters to the ground is meant to be interpreted by Parris as a threat on his life - and a well-deserved one at that. Parris has participated in the wrongful accusation and conviction of many Salemites.
Symbolically, a dagger is an instrument of violence - something one would use to inflict harm upon another. Reverend Parris is similarly an instrument of violence and death. His selfishness in trying to protect his reputation in the community by eliminating his enemies has precipitated the deaths of innocent people.