Groups of individuals may be specified for Trade
Here the girls (who happen to be centers, and could be
specified as such)
walk forward to take each other's places.
In the wave they were holding
left hands; use those
joined hands as a pivot to trade places.
Other trades are possible in the wave; for example,
Boys Trade (or
"Ends Trade") or a hand could be specified:
"With the right hand, Trade".
For more on Trade (there are MANY ways to trade) click here: