They Might Be Giants like to change the lyrics of their songs when they perform them live, both to amuse the crowd and to keep from getting bored playing the same songs over and over again. One of the lines in "Why does the sun shine?" is almost always improvised.
The original line is:
Scientists have found that the sun is a huge atom-smashing machine. The heat and light of the sun come from the nuclear reactions of hydrogen, carbon, nitrogen, and helium.
Some alternates listed on TMBG.org include (In progressively weirder order):
Scientists have found that the sun is a huge atom-smashing machine. The heat and light from the sun come from the nuclear reaction between oxygen, hydrogen, helium, and hydrogen.
You know, Frank, scientists have found that the sun is a huge atom-smashing machine. The heat and light from the sun are caused by the nuclear reaction between hydrogen and you, Frank O'Toole.
Scientists have found that the sun is a huge atom-smashing machine. The heat and light from the sun come from the nuclear reaction between hydrogen, nitrogen, helium, carbon, boron, chloron, fluoron, moron, and estrogen.
When I saw them in concert they used the following:
You know, scientists have found that the sun is a gigantic atom-smashing machine. The heat and light from the sun come from the nuclear (nuclear! nu-clear!) reactions of estrogen, estrogen, estrogen, estrogen, estrogen, estrogen and estrogen!
At the end of the song he had a little lesson on the proper pronunciation of the word nuclear. He explained this was provoked by him hearing Dubya mispronounce the word nuclear three times on TV the night before.