At one point last summer when I was at my parents place. I was out in
the garden and found a white plastic tub with some water and
stones in it. I believe that the water was ment for the dog.

 I didn`t think much about it, but after a while I started to place some other
stones in there, and relate the water and the stones to each other.

After a while, when I was doing something else and had forgotten about
the stones, my parents came out in the garden and as they passed the
plastic-tub, they both reacted on it and became really confused about it.
The same thing happened when my aunt and her husband came by a few minutes later.