I quite like this saying. I have been fooled twice a fair few times. Above is a tiny, single-celled, creature called Stentor. They are only about a millimetre long. For a single-celled creature this is huge, but it is still pretty small.
But despite the fact they have only a single cell, not the trillions we have, they can learn. This is shown in the harm-avoidance response. When exposed to a sudden jet of water (they live underwater in pools) they retract away from this. But if no harm comes from this, when exposed to a second jet of water they do not retract.
Pretty smart for something so small it is hard to see with the naked eye. I read about this in Wetware, a book by Dennis Bray. It is about how even single cells can effectively compute responses, in this case to a external stimulus, and have, in effect, a simple memory that enables them to learn. In this experiment Stentor learns not to waste effort responding to something that was harmless last time.
Bray’s perspective here is that we naturally associate memory with our brains and their network of nerve cells, but much simpler structures inside cells, including our own, can in effect store information on what they experienced in the past.