Ca²⁺ drop in single cells. (A) Ca²⁺ signals from three different cells (depicted in three different colors) evoked by paired cGMP flashes (dashed lines; Δt = 800 ms). (B and C) Representative swimming paths and corresponding Ca²⁺ signals from single cells after a single flash (B, yellow box and black flashes) or two flashes (Δt = 800 ms; C, yellow boxes and black flashes). The head (blue traces) wiggles around the average path (black trace). Swimming direction is shown by red arrows. After the second flash (C), the swimming path transiently bent in a clockwise direction, whereas the control cell swam undeviated (B, gray flash).