1 Jamie: Hey Adam, did you know that tree frogs secrete an adhesive so that they stick together during copulation?
2 Jamie: Biologists tried removing the gland that makes it, and found the frogs couldn't reproduce without it.
3 Adam: Really? What's the chemical formula?
3 Jamie: C₅H₈NO₄Na.
4 Adam: You mean they need a monosodium glutamate?

Monosodium glutamate is a sodium salt of glutamic acid, which is one of the basic amino acids that play a fundamental role in our body chemistry and cellular metabolism. Glutamic acid is essential for the proper functioning of the body, and is in fact the most common neurotransmitter molecule in the human nervous system.

It's not necessary to take in glutamic acid though, as the digestion of proteins in our food produces it as a byproduct. From there, it plays an important role in the elimination of nitrogenous waste, binding it into urea for excretion.

Glutamic acid is also responsible for producing what has recently become known as the fifth basic taste sensation, along with the more well-known salt, sweet, sour, and bitter: umami. It is a key flavour traditionally identified in Asian cuisine, which makes heavy use of ingredients naturally rich in glutamates, as well as the manufactured flavouring agent monosodium glutamate.

There are some health concerns about the use of added monosodium glutamate in food, with research appearing to indicate that some people are susceptible to annoying symptoms after eating food containing it, but the jury is still out over any longer-term effects. One of the greatest dangers cited is the probability of attracting the attention of amorous tree frogs after a Chinese takeaway meal.

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2015-06-26 Rerun commentary: There's no link to information about umami above, because the Wikipedia page for umami was not created until after this comic was originally published. Umami was only really beginning to get any mainstream attention and published information around then - less than 10 years ago.