Why do we brain "fart"?

Brain farting, is a special slang for abnormal brain activity which results in human error while performing a repetive task,or more generally denoting a degree of mental laxity or any task-related forgetfulness, such as forgetting how to hold a fork. A brain fart is usually by loss of train of thought and saying something fantastically stupid without realising it.A gap, interruption, or uncontrolled shift in a chain of thought resulting in a lull, pause, and/or blank stare during oral communication and sometimes involving the loss of short term memory.