Extreme pain is experienced, often with vocalisation; 
The UK only has three native snakes – the Grass snake, the Smooth Snake and the Adder (viper) Of these, only the Adder is poisonous.
The Grass snake is recognised by the green/yellow and black markings on the back of it’s head. It rarely bites but can look aggressive if cornered but it’s bite is not poisonous and would show as horseshoe shaped teethmarks.
The Smooth snake is very rare in the UK and normally only found in the Southern Counties. Again, like the Grass snake, it is not venomous but can sometimes be mistaken for an Adder because at first sight, it can look similar, although it lacks the solid zig zag markings of the Adder.
The adder is easily recognisable by it’s zig zag pattern.
Snakes in the UK are protected under the Wildlife and Countryside Act 1981. All UK snakes hibernate between September/October and March, when temperatures fall below 9 celsius. During warm weather, snakes are active during the day although very rarely seen because they slink off as soon as they feel the vibration of something approaching.
Adders are not aggressive snakes and will normally only strike if they are harassed or feel threatened. Quite often an inquisitive dog can fall foul of the Adder because he has stopped to investigate this strange creature. If not treated promptly and effectively, a bite from a venomous snake can be fatal to a dog.
Extreme pain is experienced, often with vocalisation;
Fast action by you could save your dog’s life.