Thanks to Leaky we have a rumoured description of the Half-Blood Prince teaser trailer!

The report says again that the trailer is still tentatively attached to Prince Caspian/Narnia on the 16th, and that the trailer will clearly show the darkening tone of the series, “with footage of the attack on the Burrow” as evidence of this. Reportedly, trailer shots will include a taunting Bellatrix, Draco on the train, Slughorn, Snape in a pivotal moment, Dumbledore in the cave, and clear evidence of the developing Harry/Ginny relationship. There are also quick glimpses of Quidditch, the Trio, and a bit of humor from Ron.

Remember this is NOT confirmed, so treat it as a rumour until we get confirmation from WB.