Holborn Station

At Holborn station, on the stairs
I came upon them unawares
Two days this week I found a sock
While hurrying to beat the clock
So if you have a little child
Who likes to let his toes run wild
This may be where he sets them free
Or, otherwise, the truth may be
That when you wash, and half the pair
Disappears to who knows where
They sink through drains to underground
Where, deep beneath the earth, they're found
In the Tube, in tunnel lairs
Except for these, caught on the stairs
And that's not all I've seen that's strange
Upon the Holborn interchange...