Famous first words - the moments leading to defect discovery

Just a fun little thought of the day from today...

There's a well-known phrase that people use - "Famous last words". Often it's in this context:

I was thinking about my inner dialogue today during testing, and I realized that every moment just before finding a bug, I'd catch myself saying one of two phrases. I'm going to call them my Famous First Words, because they define the first moment when I know I'm on to a defect. I'm sure many testers can relate to these moments.

"Hey! I wonder what happens when..."

I'd say this is the more common one. It usually happens during exploratory test sessions. I'll be working through testing the feature as normal, and out of nowhere this thought occurs. It's like being able to tell ahead of time that an area is just asking for there to be a bug. "I wonder what happens when I enter this value..." BOOM! - Exception occurs.

The other phrase happens a little more out of my control:

"Hey! That was weird..."

This one happens after catching a glimpse of some action (or lack of action) that occurs. It's when a dark corner of my brain lights up and says "I've seen this before" or "Did that just...?". This one is neat to me because it's those little details that the untrained tester may miss. When just a flick of uncertainty pops up for a brief second. This phrase has led me to find countless threading/asynchronous issues and things that are just subtle enough they weren't caught in your average, functional testing.


These are just to two I seem to notice most commonly in my day-to-day testing activities. Are there any other internal phrases that people find are precursors to finding defects?