In forensic identification, it is crucial to know whether a specific technique, for example, hair analysis, can actually measure if one hair matches another one. If the technique doesn't do a good job, it means it has:

You can drink laxative, or  do this exercise when you are sitting in the bathroom on the toilet. to relieve  constipation  fast or in about 1 minute, pinch your nose after your usual exhalation. start holding your breath. but do not mouth breath during this just hold your breath. 

Basically create a schedule on what you need to study and stick with it