What is the point of Tesman constantly saying "What?" throughout Hedda Gabler?

Tesman is the proverbial absent-minded professor, a scholar who is fixated on intellectual matters. His constantly saying "What?" is emblematic of his remoteness from others, including Hedda, and of his being disconnected in some way from the outside world and from other people's concerns. He either doesn't hear or doesn't understand much of what is going on around him.
Why is this significant to the plot of Hedda Gabler? For one thing, Hedda and Tesman are mismatched. She is not the sort of woman who needs a man whose head is in the clouds, and his absent-mindedness is really of the sort that would probably drive any person crazy. Her marriage is a source of deep dissatisfaction to her, creating a situation where she's vulnerable to other possibilities that present themselves. Ejlert is still in love with her, and Brack is interested as well (in his unscrupulous way).
But the odd, disconnected behavior of Tesman is merely a kind of superficial manifestation of the deeper source of Hedda's unfulfilled life. Hedda's unhappiness arises from an existential conflict with the workaday world around her. Even her playing with guns and the recklessness it indicates is a sign of a desire to escape from the mundane existence in which she finds no happiness. Tesman's rather goofy and stilted actions are only a single element of what pushes Hedda over the edge and makes her take her own life rather than continue in a world she finds meaningless.