Hi Grey ,
Rob uses Swing here as a verb , and of course a verb doesn't have a plural but Swing as a noun does have a plural :
swing (singular) swings ( plural )
March 25, 2008
To be honest there is no plural of swing!
"They swing in the breeze!"
this describes more than one thing.
but for some things you can say swings!
the pendulum swings quickly!
Hope that helps