In the Cheers episode "Endless Slumper" (S01E10)" there are a couple of scenes where Sam (Ted Danson) displays a bar slide trick where he is able to curve the glass around the corner of the bar. The scene where he first demonstrates this can be seen below. Its actually really quite amazing.
My question is, is this a real trick? Is he actually able to curve a glass like that or was there some kind of visual or special effect in play to make it do that?