Rodent Roadsigns
Mice can retrace their steps because they arrange objects to help them remember where they have been, say researchers.

These rodent "roadsigns" - piles of seed shells, leaves and other small objects - could be the first evidence of such sophisticated behaviour in any mammal apart from humans. The phenomenon was uncovered by researchers at Oxford University, UK, who noticed that wood mice tended to move piles of small objects, then return to them frequently. They had the theory that these were primitive landmarks, designed to help them forage for food efficiently. To test this idea, Drs Pavel Stopka and David MacDonald brought eight wild mice into a controlled environment inside a laboratory and left them to explore it. [BBC]

Nature... ah what can I say, never ceases to amaze me... Btw, who all have watched Mouse Hunt? I loved that flick.