Q. This is probably not a question for a rabbi, but you might be able to help me out: Why do people clink each other’s glass when they drink a toast?
Deuteronomy 32:33 says, Chammat tanninim yeynam – “serpents’ venom is their wine”.
Putting poison in someone’s drink in order to kill them must have happened often. A host could prove that the wine was not poisoned by pouring some of the guest’s wine into his own glass and drinking it first to show there were no ill effects.
If you trusted your host you would drink from your own cup straightaway and both would clink their glasses against each other.