'Downton Abbey' photo features plastic water bottle

CHICAGO (WLS) -- Can you spot the mistake?

This publicity photo promotes the upcoming fourth season of "Downton Abbey." But look closely, above the fireplace.

That's right; it's a plastic water bottle. Since the series is set in the 1920's, it's very much out of place.

And as some have suspected on Twitter, it's either a very stupid mistake or a brilliant publicity ploy.