The Amazing World of Gumball (2011)
S3E4 The Joy
Miss Simian notices that Gumball and Darwin are unusually happy on Monday, prompting her to suspect something is off. She decides to run some tests on them, but the school nurse expresses her disapproval of the methods. Before long, Gumball and Darwin inadvertently spread the 'Joy Virus' throughout the school, leading to chaos. Now, it's up to Miss Simian, armed with her trusty tape player, to find a way to restore order and save the other students from this infectious happiness.