Congress hears testimony again on GameStop, focusing on the financial plumbing behind the frenzy.

The House Financial Services Committee is holding its second hearing on the GameStop frenzy on Wednesday. A number of experts are expected to explain what the saga says about plumbing in the stock markets.

The hearing is likely to have a shakier tone than the committee’s first hearing on GameStop, which saw the spotlight on Robinhood, the trading app at the center of a notable rally that saw shares of the struggling video game retailer jump over 1,600 percent in January,

Witnesses include stock exchange officials, market analysts, former regulators, and academics. Prepared testimony suggests that the Witnesses will focus on what, if any, flaws in the American stock trading system have been uncovered by the surge in trading in GameStop.

Sal Arnuk, co-founder of trading company Themis Trading, plans to highlight the growing role of payment orders, with retail brokers like Robinhood passing customer orders to specific trading companies in exchange for payments.

“These practices create a massive incentive for such brokers to sell their client orders to highly developed trading companies that can benefit in a unique way,” Arnuk will say, according to preliminary statements by the House Committee. “This is an unnecessary conflict that can harm retail investors and undermine the integrity of the entire market ecosystem.”

Other witnesses such as Alexis Goldstein, senior policy analyst at Americans for Financial Reform, will underscore the growing dominance of trading firms that retail brokers pay to carry out their orders.

Two major market makers, Citadel Securities and Virtu Financial, “execute larger volumes of US stocks than the New York Stock Exchange,” she said in prepared statements, urging regulators to look into whether their growth has worsened available prices Investors on the public exchanges.

The hearing is scheduled to start at 10 a.m. Other attendees include Michael Blaugrund, Chief Operating Officer of the New York Stock Exchange; Vicki L. Bogan, Cornell University professor specializing in household financial and investment behavior; Dennis Kelleher, Better Markets’ chief executive officer, who advocates market reform; and Michael Piwowar, executive director of the Milken Institute Center for Financial Markets and former SEC commissioner.