One would dig a hole and the other would follow behind her and fill the
hole in.
They worked up one side of the street, then down the other, then moved
on to the next street, working furiously all day without rest, one girl
digging a hole, the other girl filling it in again.
An onlooker was amazed at their hard work, but couldn't understand what
they were doing. So he asked the hole digger,
"I'm impressed by the effort you two are putting into your work,
but I don't get it -- why do you dig a hole,
only to have your partner follow behind and fill it up again?"
The hole digger wiped her brow and sighed, "Well, I suppose it probably
looks odd because we're normally a three-person team. But today the girl
who plants the trees called in sick."
ah dear 
I think I may be turning blonde.
You are certainly making me curious! 