Earlier today a discarded party balloon on a stick delayed a Jubilee line train at Canada Water station.
It had become trapped between the train and the platform doors and one of the latter was unable to close. It was almost comical... the door was constantly opening (a few inches) and closing but it was unable to close completely.
Both I and another passenger on the train had seen the balloon there before the doors closed but we both assumed that it would either be burst by the closing doors or (once we realised that it was going to be stuck between the two sets of doors) we thought that the departing train would burst it. This explains why we had not retrieved it whilst the doors were open.
During this time there were automated announcements telling passengers to not obstruct the closing doors, but since the doors on the train had fully closed we were powerless to remedy the situation.
In the end the train driver walked long the train and took the offending balloon away.
Sorry, this happened so quickly that I did not get to film it.
As an aside, despite the delay this train still ended up being held at West Ham to 'regularise the service' AND having to queue up to enter Stratford station.