To the left, to the right!

I posted a photo of this plant on Facebook, to see whether anyone could tell me what it was* and more importantly, why it behaves as it does...
On Tuesday morning, it was pointing to the left.
On Wednesday morning, it was pointing to the right.
On Thursday morning, it was pointing to the left.
It wasn't following the sun, because it changed direction during the night. 
Nor was I walking round to photograph it from the other side!

One friend wrote: "Think actually this is the Great Yellow Pointy Plant. It is the only member of the vegetable kingdom capable of recognising Roman letters. Points to right on days beginning with a 'T', to the left on all other days except Fridays, when it points to the nearest pub."
I rather suspect said friend may well have already visited the pub!

* They did: it's a verbascum ... but nobody can explain the pointing behaviour!