My dad has been a local entertainer/ventriloquist/magician/clown for about 50 years. He still does about two shows or birthday parties every weekend as Jingles the Clown.
He recently developed a cough that just won't go away. At first it was a bronchial thing and when that cleared up and he kept coughing, they found he has a hiatal hernia. Hiatal hernias, while not usually associated with comic moments, can lead to unexpected fits of giggles.
While we were out shopping today, my dad called my mom. She asked him how his party went and if he coughed much. He said he was fine for most of the party but during the audience participation portion of his magic show, he told the kids, "Repeat after me: Hocus pocus *cough, cough*..."
The kids responded, "Hocus pocus *cough, cough*..."