What did Tom show off in front of the new girl?

From the text:

He worshipped this new angel with furtive eye, till he saw that she had discovered him; then he pretended he did not know she was present, and began to “show off” in all sorts of absurd boyish ways, in order to win her admiration. He kept up this grotesque foolishness for some time; but by-and-by, while he was in the midst of some dangerous gymnastic performances, he glanced aside and saw that the little girl was wending her way toward the house.