Water jets

This feature at The Newt has jets of water being fired from the toads when sensors are triggered.

The sensors are located in recesses and seemed to be sensitive to light, or rather, the lack of it. If it were an LDR, dark would mean high resistance so could change a logic gate. The jet sprayed as soon as the sensor was covered. It wasn't triggered on the release back into light. It occurred to me that there would be a problem with this at night so either there is an overall timer or I am wrong and it is about beam breaking.