Clink the glasses………?

Why do people clink their glasses before drinking a toast? 

It used to be common for someone to try to kill an enemy by offering him a poisoned drink. To prove to a guest that a drink was safe, it became customary for a guest to pour a small amount of his drink into the glass of the host. Both men would drink it simultaneously. When a guest trusted his host, he would then just touch or clink the host’s glass with his own.