The Collaborative International Dictionary of English v.0.48:
Byplay \By"play\, n. Action carried on aside, and commonly in dumb show, while the main action proceeds. [1913 Webster]WordNet (r) 3.0 (2006):
byplay n 1: incidental activity performed by an actor for dramatic effect; "his business with the cane was hilarious" [syn: business, stage business, byplay]