Never ending shampoo

Moved into the house last October and the previous owners left this bottle of Tesco's tea tree shampoo along with a very dirty shower and oven, but lets not dwell on that. The shampoo was used regularly but it never appeared to run out. I had thought it reproduced itself at night but its emptiness today suggests that was just hopeful thinking. Am sorry this reminder of the 1 October 2010 has no all gone.