I was measuring my tank one day and my fish freaked right out. I told my friend and he said his fish freak right out when they see a tape measure. I tried it again tonight and yup they freak right out.
Try it out do your fish freak out when you measure your tank?
So a guy walks into a Pet Store
Guy: "I have Algae on my drift wood!"
Pet Clerk: "Take two Plecos and call me next week."
I've never had a problem with them personally, but whenever I would scare my mbunas into the rocks, I could get them out super fast just by pointing a laser onto the sand -- they went nuts trying to get that thing.