Why is it when I first met certain girls everything goes slow motion for a short amount of time?

This has only happened to me 3 or 4 times so far but I always end up going out with them in the future. Is there a reason for this and is it normal? The slow motion doesn't last for that long, no longer than a minute.Why is it when I first met certain girls everything goes slow motion for a short amount of time?ahh i love when women run in slow motion