Search round in the garden, you're bound to find a

Snail

Perhaps you've always wondered why they leave a sticky trail?
Some people think it's meant for friends, to show which way they're going
But that is not the reason why they leave a trail showing...

The answer's plain - they cannot see an inch beyond their noses
Or recognise the rockery from a bed of roses
And snails have no memories, which gets them in a mess
That's why they wear their houses, to remember their address.

And so they leave a sticky trail, strange as it may seem
Not to show the way they've gone,
But to remind them where they've been!

Can't beat a bit of Jeremy Lloyd on a Sunday afternoon