How does Hansberry develop a suspenseful mood when Bobo first walks into the younger house?

From the text:

BOBO (His frightened eyes on the floor, his hat in his hands) Could I please get a drink of water, before I tell you about it, Walter Lee?
(WALTER does not take his eyes off the man. RUTH goes blindly to the tap and gets a glass of water and brings it to BOBO)
WALTER There ain’t nothing wrong, is there?
BOBO Lemme tell you—