The concept of "nothing" is easy to grasp for most humans, but the concept of zero as a number is much harder. Recent research shows that bees can be taught that zero is a number which is less than one. This nifty explainer gives an overview.
Humans have only been using zero as a number for about 1500 years. via Vox:
But how we seized zero and forged it into a tool is still a mind-bending mystery. New research suggests the ability to fathom zero may be more widespread than previously thought in the animal kingdom. Australian scientists were able to teach bees to recognize zero as a quantity less than one, a task that confounds most human children under the age of 6. The result is kind of astounding, considering how tiny bee brains are.
Scientists believe this may help us understand how all animal cognition works, and it may in time lead to animal brain biomimicry in computing.
Photo: Muhammad Mahdi Karim [Wikipedia]