When Kripke pipes helium into Sheldon's office, he also pipes in oxygen from the green tank. As a scientist he is doing this to prevent a dangerously low level of oxygen but to still create the voice change of low-density gas exposure.
The chemical reaction that Sheldon uses to get his revenge on Kripke is a genuine one (often used in practical jokes) and is often referred to as "Elephant toothpaste". Hydrogen peroxide decomposes slowly to form water and oxygen gas. The presence of potassium iodide catalyzes this reaction, so that it produces large quantities of oxygen very quickly. The gas then causes the liquid detergent to froth copiously as shown.
Fever 104, the radio station Raj mentions, is actually one of the most popular radio stations in India.
Katee Sackhoff's appearance in this episode came about because she accompanied her Battlestar Galactica (2004) co-star Tricia Helfer when she was making a guest appearance on Chuck Lorre's other hit sitcom Two and a Half Men (2003). Lorre approached her about a cameo on The Big Bang Theory (2007). Sackhoff had previously turned down that opportunity in Season 2 when the chance of playing herself went to Summer Glau so she instantly leapt at Lorre's offer.
This is the first episode with Bernadette to feature her high-pitched voice.