The suckling glass

Now, place the glass upside down over the candle (see picture below). Be careful, do not overheat the glass! Now, press the entire rim of the glass against a smooth piece of your skin.

Why does the glass adhere your skin (or the skin of your volunteer) if you press it down?

a) The hot air in the glass cools down. The pressure inside of the glass decreases. Because of the higher air pressure outside of the glass, the skin is pressed inside of it.

b) The hot air in the glass cools down. Therefore, the pressure inside of the glass decreases. The lower air pressure inside of the glass sucks the skin inside.

c) That is of course due to the suckling-effect of the glass. Just like jam jars are suckled onto their lids.