Indiana University Police Academy in the US has a unique way to test their recruits' focus and ability to shut down their impulses while on duty.
To do that, the recruits are presented with a squeaky rubber chicken near their faces and the challenge is not to laugh as the chicken is squeezed with its hilariously funny voice.
As seen in the video, very few recruits managed to hold their laughs while others just uncontrollably burst into giggles.
Anyone who fails to keep a straight face is punished by doing planks. The test is commonly referred to as "The Chicken Test".
I am not really sure how this helps policemen later in their careers, I mean it is not like there are plenty of criminals out there who decide to choose squeaky chickens as their primary crime weapon.
Jokes aside, there are jobs in law enforcement that require applicants to remain serious and be100% immune to laughter. One notable example is the Beckengham palace guards, who are well known for their ability to resist smiling.