Cationic channel blockers reduce the ‘sneeze’ response. a. The sponge ‘sneeze’ behaviour involves contraction of the osculum (white arrows), inflation, then contraction of canals (black arrows) and recovery (bar shows canal diameter). b. Neomycin sulfate (red) and FM1-43 (blue) reduce the peak amplitude of the behaviour in E. muelleri (n = 8; p < 0.001). Gd3+ (solid green) eliminated all response (n = 3; p = 0.015), but after recovery for 24 h the sponge response was even greater than before (dotted green). c, d All three compounds caused lengthening of cilia relative to controls (left), but had no effect on choanocyte flagella (bottom right) in E. muelleri (*significance at p < <0.001; error bars show ± SE). Scale bars: a, 1,000 μm c, 10 μm.