Fig. 1. Dummies, experimental set-up and measurement of response strength. (A) The dummy's size and appearance from the side. Bold dimensions indicate the most frequently used dummy. (B) The dummy was moved along a straight line (dummy track) between two tent pegs. The observer controlled the dummy from a distance by means of a fishing line wrapped around the tent pegs and attached to both sides of the dummy. The small rectangle represents the recording area of the video camera, centred on the focal crab's burrow. (C) The crab's response strength was measured as the distance the crab moved towards its burrow during a dummy presentation (d₀-d₁) relative to the initial distance before the response (d₀).