How they do it:
For a start the cobras fangs are fixed and they cant change the size of the venom orifice, so basic fluid dynamics would lead you to think that the pattern of the fluid should be fixed, explains Young. But Young had also noticed that the snakes wiggled their heads just before letting fly. The question became how do we reconcile those two things, says Young, who publishes his discovery that the snakes initially track their victims movement and then switch to predicting where the victim is going to be 200ms in the future in the Journal of Experimental Biology on 14 May 2010. Analysing Young’s movements, only one thing stood out; 200 ms before the snake spat, Young suddenly jerked his head. The team realised that Youngs head jerk was the spitting trigger. They reasoned that the snake must be tracking Youngs movements right up to the instant that he jerked his head and that it took a further 200 ms for the snake to react and fire off the venom.