I was watching an episode of Friends where Ross talks about "counting mississippily".
I did not get the joke. Why would someone say "Mississippi" after every number? Is there some story behind it?
Mississippi is one of several phrases used to approximate one second for the purposes of informal time keeping. That is, if you count to five "Mississippily", then you've counted five seconds. Outside North America, as you might image, this is usually not very common.
In English, I've heard several different methods of doing this. E.g.
In other languages, they have similar constructs, but adjust for appropriate time. For example, in some German speaking areas, they just say "einundzwanzig" (German for 21) over and over. I find this one particularly interesting because they don't actually include the current count in the number, but rather must keep it in their head. I've heard of a variation where they start at 21 and go up. I'm not sure what happens when they hit 30, since it has substantially fewer syllables than 29.
Very good question! I've always assumed that it was for the purposes of spacing out numbers while playing hide-and-seek. If you don't ensure that the numbers are a good distance apart, then obviously the seeker just burbles "onetwothreefourfivesixseveneightninetennnnnnnnahundred... ready or not, here I come"!