Fish see illusions, just like us
Which blue circle looks bigger? They're the same size. This illusion is called the "Ebbinghaus illusion" and it turns out, even fish are susceptible to this visual trickery. Some fish were trained to prefer large circles, and some to prefer small circles. Their test choice depended on the appearance of the circle in relation to a group of differently-colored, differently-sized circles.
Baby chickens count from left to right
A new study suggests that similarly to us, chickens use a "mental number line," in which smaller amounts are expected to be to the left, and larger amounts to the right. After training baby chicks to find a treat behind a cue with five dots, they gave them a choice between two cards with five dots. They preferred to go to the cue on the left. When the two identical choices were a larger number of dots, they preferred to go to the right.
Golden orb-web spiders count their prey
Spiders appear to have some sense of how many prey they have stored, spending more time searching when more prey have been removed. Scientists tested this by controlling how many mealworms spiders were given, later taking some away, and observing what the spiders did. These findings suggested that spiders have both a rudimentary sense of quantity and size, as they also spent more time looking for larger larvae. And perhaps the results also suggest that spiders don't like it when you steal their food.