An example is in his experiments with foraging honey bees. He showed that honey bees show curiosity for yellow and blue paper models of flowers, and suggested that these were visual stimuli causing the buildup of energy in one specific centre. However, the bees rarely landed on the model flowers unless the proper odour was also applied. In this case, the chemical stimuli of the odour allowed the next link in the chain to be released, encouraging the bee to land. The final step was for the bee to insert its mouthparts into the flower and initiate suckling. Tinbergen envisioned this as concluding the reaction set for honey bee feeding behaviour.