I'll use some personal examples but different types.

Intrusive thoughts can be:

Images or "movies" that pop up in your head.

When I mop the floor at work, I get images of coworkers slipping and hurting themselves. Whenever I mess with a cardboard box, I get an image of it paper-cutting my eye. Usually followed up by fake pain in my eyes that makes me wince.

"What if?"

"What if my partner wrecks their car on the way to work?" "What if I didn't shut the back door all the way and the cat gets out?" "What if all my clocks aren't right and I'm late to work?" "What if my friend thinks I'm a creep?" "Did I feed my pets or are they starving and dehydrated?" "Do i smell bad?"

Sudden unpleasant memories

Sometimes I get traumatic memories that pop up unwillingly, but this is more related to PTSD. PTSD has intrusive thoughts too. Sometimes I suddenly remember things I regret or feel ashamed about when I should have moved on, related to real event ocd. Those "cringe" memories you get that embarrass you and come back out of no where.

Sometimes intrusive thoughts for me manifest after feeling a physical sensation or having a false sensation. Example: If my leg hair tickles my leg, I might get an image of a poisonous insect or something gross like a maggot burrowing into my skin. If I get physically/sexually aroused, sometimes it's followed up by unpleasant images like incest, violence, or p3dophilia

Hope this helps.