Things that are out of place, things that appear or disappear, odd things that really make you wonder what on earth happened while you were gone.
Two examples:
1. Today, when I got home from work, I saw 4 first-aid kits on the kitchen counter. Our first aid kits are stored in a cabinet above the sink (I know, I really do need to consolidate, but they are somewhat organized for specific injuries.) My first thought was "Oh, no. DD#2 must have injured herself before she left for school" (She won't be home for at least another hour) After looking around for bloody spots/tissue and finding no clue, I thought "What on earth did she do to herself that she took down all 4 kits?" Hmmmmm . . .
2. Last week CW came to work in the morning and said "What the heck this? Where did this come from?" There was a sizable cigarette ash in the middle of her desk. Our facility is a no-smoking building. We figure that a security guard found her desk the perfect place to take an illegal smoke break, but still . . . very odd, and Hmmmmm . . .
What about you? Have you found odd things out of place in your home, at work, or elsewhere that made you go "Hmmmm?"
edited to add a word so the sentence made sense.