True story from my school days.....
The class clown (Tommy) had his hand up and was desperately trying to get the attention of the teacher so he could be 'excused'. The teacher, however, knowing his propensity to regularly come out with something completely ridiculous and have the class burst into uproarious fits of laughter, chose to ignore him entirely and carry on with the lesson.
As time went on Tommy became more desperate and stood up in class, his frantic arm waving getting the teacher to finally acknowledge him: "Okay, Tommy, what is so urgent ?"
Tommy's (by now too late) response was: "Miss, do farts have lumps in them?"
'No Tommy, I do not believe they do!, snapped the rather annoyed and now red faced teacher.
"Well in that case, Miss, I believe that I have shit myself!!!"
Yep, you guessed it, the whole class burst into uproarious laughter and the 'formal' lesson was prematurely concluded.