There is a clear tube within all the cups but the 1st one, the last one is filled with a clear liquid the others are capped off, the tubes come up to about 2.5cm before the top of the glasses so you cant see them from the angle its filmed at, however if you look very carefully they create a different colour on his t-shirt if you look through them at it.

There is a clear tube within all the cups but the 1st one, the last one is filled with a clear liquid the others are capped off, the tubes come up to about 2.5cm before the top of the glasses so you cant see them from the angle its filmed at, however if you look very carefully they create a different colour on his t-shirt if you look through them at it.