A squirrel is busy retrieving acorns - a small hole in the grass, the husk of the acorn lying beside it = the evidence. New potholes appear on the lawn every few days. She presumably locates her buried treasure by smell: I have often seen her sniffing about the grass, and she often has mud on paws and nose. I don't think I can attribute great feats of memory to her however - grey squirrels cannot match the astounding Clark's Nutcracker in North America, which may recover 70% of its cached nuts from a territory of over 100 square miles (see article). Every year I have several oak seedlings sprouting from the lawn, which have presumably grown from the acorns that have escaped her or her fellows.
I am reminded how important smell is in the non-human world. The beetle which flies heavily past me in the garden is unlikely to be pursuing a random path. The ants which forage among the grass stems are following scented tracks laid by their fellows; the closer they come to their native ant-heap, the stronger and more reassuring must be the smell of home. The voles have their runs in the undergrowth. The moorhens are patrolling their part of the garden, reinforcing an invisible territorial boundary between their domain and that of the moorhens on the back pond. The rabbits have taken to sitting on top of the ant-hill on the lawn, and crapping there, making a pile of hraka, as Richard Adams might have put it.
My garden has places and spaces with meaning of which I know nothing. It is filled with tracks, trails, signs and boundaries; if I could read them all I would be astounded - and completely overwhelmed with the quantity and complexity of the information. I just filter out what is important to me - and the other inhabitants do the same.