A Viper (or Adder) has this marking on his head and neck; other snakes have none—in Great Britain.
As far as snakes go, there are not, fortunately, many poisonous ones in England—only the viper is poisonous. It is differently marked from other snakes having a black V or arrow-head mark on its head and a dark zig-zag line along its back. It is generally dark brown in colour. The viper is sometimes called adder.
Of course a scout ought to know about snakes because in almost all wild countries you come across plenty of them and many of them dangerous.
They have a horrid knack of creeping into tents and under blankets, or into boots. You will always notice an old hand in camp before he turns in at night look very carefully through his blankets, and in the morning before putting on his boots he will carefully shake them out. I even find myself doing it now in my bedroom at home, just from habit.
Snakes don't like crawling over anything rough as a rule; so in India you often construct a kind of path made of sharp jagged stones all round a house to prevent snakes crawling into it from the garden.
And on the prairie hunters sometimes lay a hair rope on the ground in a circle round their blankets.
A hair rope has so many tiny spikes sticking out of it that it tickles the snake's tummy to such an extent he cannot go over it.
I used to catch snakes when I was at school, by using a long stick with a small fork at the end of it. When I saw a snake I stalked him, jammed the fork down on his neck, and then tied him up the stick with strips of old handkerchief, and carried him back to sell to anybody who wanted a pet. But they are not good things to make pets of as a rule because so many people have a horror of them, and it is not fair, therefore, to have them about in a house where servants or others might get frightened by them.
Poisonous snakes carry their poison in a small kind of bag inside their mouths. They have two fangs or long pointed teeth, which are on a kind of hinge; they lie flat along the snake's gums till he gets angry and wants to kill something; then they stand on end, and he dives his head forward and strikes them into his enemy. As he does so the poison passes out of the poison bag, or gland as it is called, into the two holes in your skin made by the fangs. This poison then gets into the veins of the man who has been bitten and is carried by the blood all over the body in a few seconds, unless steps are at once taken to stop it by sucking the wound and binding the veins up very tightly.