"Maybe stuff's getting squished inside you and moving along faster than usual. ???"
Your actualy right. When a person does abdominal exercises, it causes the digestive tract to move a little. For some people, it will cause the gas in their system to pass quickly. For others, it causes their bowls to be moved along the digestive tract faster. This does not happen to everyone, but for a few.
I guess I'm lucky. I never do stomach exercises. I've had the V shape obliques and a flat, hard stomach since I was about 16. It's just in my genes. But when I do - do stomach exercises. I'm a ticking gas bomb waiting to go off.
For the majority, weightlifting is a harmless past time. But for the elite, it's a grueling ritual. It incorporates pain as it's own divine reward. It sees no amount of crushing dedication as too great a sacrifice and never fails to render results.