I've had this too - just put it down to as GurnE says, you just looked twice in one second. It's a bit hit and miss because your first look needs to be right at the beginning of the second, and then again right at the end.

What you will normally see (therefore get used to) will be looking at it half way through, so it's only half a second before it moves.

So, every so often when you look round quick, you'll catch it right and believe you have the power to alter time...

Make sense?