Hiccup: I believe hiccup is caused by changes in temperature in the regions above and below the diaphragm.  As we know changes in temperature causes current. This current moves the diaphragm resulting in a hiccup sound.  In Physics heat transfers from the object with higher temperature to the object with lower temperature until equilibrium is reached.
Q1=M1 C1 (T2-T1) and Q2=M2 C2 (T2 – T1)
Q1 = Q2
M1 C1 (T2-T1) = M2 C2 (T2 – T1).

When temperatures on both objects become equal then Hiccup may stop.

You can try my technique to stop hiccup, make your hands cold with ice and put your hands under your diaphragm (under the chest), it stopped my hiccup instantly !