The custom of clinking glasses comes from the Middle ages. Before drinking, the wooden mugs were hit together so that a small amount of liquid would pass from one mug to the other, therefore ensuring that your host would not attempt to poison you.
Another way to have poison free night was that the guest would pour a small amount of liquid into the host's glass. Both men would drink it simultaneously. When a guest trusted his host, he would then simply touch or clink the host's glass with his own.
Other people prefer to say that this custom was simply for the purpose of scaring off evil spirits by imitating the sound of church bells.
Even if it's common practice to look in everyone eye and clink glasses when participating in toasts among a large group, it is best to raise your glass and make eye contact with the group.
- Source 1: Web searches
- Source 2: Collected via email
- Source 3: Wikipedia