Coin through a shot glass Magic Trick?

I was at a party last night where a guy used a towel, a coin and a shot glass. He placed the towel over the shot glass, and had me hold the coin over the shot glass but under the towel, and then “drop” the coin into the shot glass that was half full of liquid. I heard it clink, but when he pulled the towel away, the coin was under the shot glass. I watched him do it about a dozen times, and still have NO CLUE how he did it! Please let me know if you have any clue