To a child, that's a huge hole, enough to swallow them.
I can only guess to My Son it was the noise, or the splash of water on the butt that startles them.

It’s the same exact situation with my son. He’ll be five this month and it has gotten better in the past six months or so. He kept saying he was scared to go, perhaps he was afraid it would hurt or maybe it did hurt. We don’t know for sure because he’s non-verbal. But he would scream and cry and kept saying “scared”. As you probably know, there is a correlation between gut health, gastrointestinal problems and autism.

My son sees a pediatric gastroenterologist and she thought he might have an impaction so he underwent a colonoscopy. He did have quite of but of dried fecal matter and after he was flushed out his potty situation has improved. We also give him Miralax everyday and sometimes Exlax when he was badly constipated (if he hasn’t gone for several days). We also tried epsom salt baths and other homeopathic remedies.

Talk to your pediatrician about seeing a specialist. It has gotten better for my son but he still has issues as he is potty trained to go pee but not poop, and we still have to intentionally put him on the potty and convince him to go.

Snacks, Songs, Toys that stimulate Laughter, Shower/Bath as a Reward.