Usually to check if a person is dead, one checks their pulse and breathing. If you want to fake your death properly, you must be able to stop both of these. You can easily hold your breath, but how can one stop their own heart? The answer lies in a ball.
If you wedge a tennis ball, squash ball, baseball or any small but firm ball in each of your armpits and squeeze tightly, the pulse at your wrist will disappear. This pulse is the radial pulse, and the radial artery is a branch of the brachial artery further up the arm. If a ball is squeezed in the armpit, it compresses the brachial artery, stopping the blood flow to the radial artery and obliterating the radial pulse. Most people who are not medical professionals tend to use the radial pulse for taking a pulse, so this method can be used to make it look like you do not have a pulse. But as this trick only causes the radial pulse to disappear, it is ineffective if the other person takes the pulse at another site such as the carotid artery or femoral artery. However, if you can control the situation and the person checking to see if you are alive is not a doctor or nurse, then it is quite a useful trick to use.