What kind of snake?

My guess is an Adder. It would make sense that it would be a poisonous snake found either in England (where I, Claudius was made) or in Europe (where I, Claudius took place). The markings are quite similar, but different enough to make me wonder. But the Adder is the only poisonous snake in the U.K.

http://www.herpetofauna.co.uk/adder.htm

Who cares what type of snake it was, but it sure did a good job during its 15 minutes of fame!

I'm no herpetologist and I'm not sure I recognize the exact breed of snake.

From the shape of the head I know that it's some variety of pit viper (a family which includes the rattlesnakes). I'm not aware of any other group of snake that shows that distinctive triangular head. The pattern on the back may not have looked natural to you, but it very well could be one of the three varieties of diamondback rattlesnake native to the southern US and Mexico.

• The eastern diamondback rattlesnake, a venomous pitviper species found in the southeastern United States.
http://en.wikipedia.org/wiki/Crotalus_adamanteus
• The western diamondback rattlesnake, a venomous pitviper species found in the United States and Mexico.
http://en.wikipedia.org/wiki/Crotalus_atrox
• The red diamond rattlesnake, a venomous pitviper species found in southwestern California in the United States and Baja California in Mexico.
http://en.wikipedia.org/wiki/Crotalus_ruber

Different species of pitvipers (all of them venomous) can be found in the New World from Canada to Argentina, and from southeast Asia to India.
(Note: None of these are native to Europe.)

• Here is the Common European Adder (or Common European Viper) mentioned in another post.
http://en.wikipedia.org/wiki/Vipera_berus

Personally, I don't think the European adder shows the distinctive triangular head seen on the snake in the opening titles. The diamondback rattlesnakes do. However, as someone else already pointed out, the adder is the only one of these that is native to Europe.

Please let me know which you think is the most likely candidate for the snake on the mosaic.

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Have you noticed that in Shakespeare's plays soothsayers said the sooth, the whole sooth, and nothing but the sooth?
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Common European adder (Vipera berus), definitely. They are a real nuisance around here.