Looking at this picture you may well feel that the arrangement would have benefited from a greater degree of symmetry.  Should that tall green thing on the right not have been balanced by a similar green thing on the left.  And by Jove there's a planter it could have gone in.

Up until Saturday night your aesthetic sensibilities would have been satisfied but during the hours of darkness the leftmost plant walked.  A few dead leaves lay strewn by the lift door on Sunday morning and the plastic inner plant pot lay forlornly in the lift.  But of the plant inside or outside the building there was no trace.

Now it wasn't a Triffid so it didn't walk of its own accord.  I suspect that one of those joyful inebriates who thinks it's a jolly jape to put traffic cones on the heads of statues emerged from a neighbouring flat and swiped it.

If I get my hands on him (or her don't let's be sexist about this) I'll take pleasure in planting its twin just where it hurts.