Fig. 1. Experimental situation and variables used. (A) A dead fly is attached to the lower side of a disk at height h above the water surface. When dislodged by the powerful water jet of an archer fish, it takes off passively at a horizontal speed _hor and will hit the water surface at point P in a horizontal distance d. (B) The same situation as in A viewed from above, showing another archer fish nearby. After a quick initial turn the second fish has aligned itself in the direction indicated by the dotted line, on which it will then rapidly accelerate. At this time the fly is still on its ballistic path above the water surface. Two errors e and e' were analyzed in order to determine whether the fish rushes in the direction of either the later point of impact P or of point P', the horizontal projection of the target's position at the end of the turn. e(e')<0 if distance O—S<O—P(P'), where O is the initial target position and S is the point of intersection between the path of the fish and the fly (horizontal projection).