Explain xkcd: It's 'cause you're dumb.
Title text: In fact, one of the boxes is full of Staphylococcus. The wrapping paper is coated in E. coli, though, so it's an understandable mistake. You know, we should really stop accepting gifts from that guy.
The first present Megan opened contained a home biology lab kit, including the equipment needed to perform a Gram stain.
Gram staining is a technique used in microbiology to separate bacteria into two broad categories based on the structure of their cell walls. The sample is treated with two different dyes: first a purple dye, then secondly a pink one. When subsequently examined under a microscope, "Gram-positive" bacteria retain the purple color of the first dye, whereas "Gram-negative" bacteria do not, allowing the second, pink, stain to show. All Megan's presents have been stained pink, and are presumably therefore Gram-negative.
In the process, she has damaged the other presents, hence Cueball's wish that she had opened another present first.
The title text refers to two bacteria commonly used as controls to confirm that the technique has been correctly performed:
Staphylococcus aureus (Gram-positive) and
Escherichia coli (Gram-negative). Neither are bacteria you want to be coming into contact with in any substantial quantities, hence the need to stop accepting presents from "That Guy".
- [Megan pouring a bucket of purple liquid on the presents at the base of a Christmas tree.]
- [Megan pouring a bucket of pink liquid on the presents at the base of a Christmas tree.]
- [Megan looking at the soaked presents.]
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- Megan: All my presents appear to be Gram-negative.
- Cueball: I wish you hadn't opened the home bio lab kit first.
I would buy one for the people I know, but they apparently cost 140$ upwards. Randall is a rich man. Davidy22[talk] 08:23, 24 December 2012 (UTC)
- 've restored the capital G's: the stain is named after
Hans Christian Gram, so should be capitalized. 18.104.22.168 09:19, 25 December 2012 (UTC)
Do E. coli bacteria mask the response of Staphylococcus? Do the responses go through the gift wrapping? The gift from the guy should have shown Gram-positive, because of Staphylococcus. Thus the mistake. --22.214.171.124 13:08, 25 December 2012 (UTC)
Of course, the dye used in Gram-staining is DYE and will color hands, clothing, (wrapping) paper, and floors. Megan might not have a bunch of bacteria coated presents (except for the one from That Guy in the title text), and instead she has just ruined her own Christmas. Or made it more awesome, YMMVFredG (talk) 16:50, 25 December 2012 (UTC)
- Given that she colored the wrappings, most presents should be still fine. Especially considering you usually wrap the present INCLUDING the original packaging. -- Hkmaly (talk) 09:27, 27 December 2012 (UTC)
I found this funny, especially with it seemingly be tangentially related to Depth-First Search (DFS). Genux (talk) 00:42, 26 December 2012 (UTC)
Most species of Staphylococcus (such as S. epidermidis) are harmless; most strains of E. coli (with the notable exception of O157) are harmless. --Prooffreader (talk) 09:13, 26 December 2012 (UTC)
Is it just me or does the one on the left on the third frame seems to be purple (Gram-positive)? 126.96.36.199 02:35, 2 January 2013 (UTC)
I just noticed that her hands are stained purple in the last frame. 188.8.131.52 16:12, 4 January 2013 (UTC)
- I don't know...they look pink to me.--Dangerkeith3000 (talk) 22:30, 7 January 2013 (UTC)
In mine they are pink (might be your monitor), and if you compare the second and third frame the striped present is not purple (Gram-positive) it is in fact pink as the rest (just dark due to the stripes on the wrapping paper). My question is why are her hands not stained purple in the second panel/frame... is she more careful with the first dye and not the second? Also, with "that Guy" referring to Santa are they implying that he pets his Reindeer and they have E-Coli on them like any other animal (lack of hands to try to wipe it away). ~~MIRAnger
Wait, why is 'That Guy' White Hat? Surely it should be Black Hat due to his habit of posting bobcats... 184.108.40.206 07:45, 31 March 2015 (UTC)
- I was wondering about that... Just some random derp 11:25, 30 April 2015 (UTC)
- ...okay, I went and changed it because it was bothering me. Just some random derp 16:35, 2 May 2015 (UTC)
It also appears that Megan skipped the necessary decolorizing step (ethanol or acetone) that prevents the purple dye from obscuring the pink for Gram negative cells. Dumping the dyes onto presents would not require this step, but it would also not provide any insights into the "cell wall" of the presents. Also she missed an opportunity to do something ridiculous with intoxicants and/or solvents! Perhaps Megan didn't read the instructions carefully, in addition to whatever weirdness led her to dump dyes all over the wrapped presents.
--Spencer9 (talk) 18:43, 16 May 2015 (UTC)