In the teaser of the episode When She Was Bad, the character of Xander is seen licking an ice cream cone. Willow and Xander exchange a few lines and then Xander puts ice cream on her nose. He'll then take a long time to wipe it off and then move in for a kiss. When he backs away you can clearly see there is no ice cream cone. He could not have eaten it because the camera was on his mouth the whole time. It's not on the wall where it could have ended up, the camera shows that too. It's not on the ground where he could have dropped it, we see the entire area surrounding him in that scene. The ice cream cone disappears and is never seen again.