irrational
Explanation
The Joke
The comic depicts a family of numbers. The number 3 (the mother) announces to the number 1 (the father) that their son, the number 2, has come home from the war but has "become irrational." The father is shocked, exclaiming "What?! Not 2! He was always... Oh my God!" In the final panel, the son is revealed -- he is now the square root of 2 (written as a radical sign over the number 2), and the father cries out "He has been radicalized!"
The entire comic is built on a series of mathematical puns. In mathematics, the number 2 is a rational number (it can be expressed as a ratio of two integers). However, the square root of 2 is famously one of the most well-known irrational numbers -- it cannot be expressed as a simple fraction. So by becoming the square root of 2, the son has literally become "irrational."
The Humor
The punchline delivers a double meaning with "radicalized." In common usage, "radicalized" means someone has adopted extreme political or ideological views, which fits the war veteran narrative. In mathematics, a "radical" is the symbol used for square roots. So the son has been both politically radicalized (in the metaphorical narrative) and mathematically radicalized (literally placed under a radical sign). The earlier setup of "irrational" works the same way -- emotionally irrational (as in a war veteran with trauma) and mathematically irrational.
The comic also plays on the trope of a family worried about a loved one returning from war changed. The visual of anthropomorphized numbers acting out this dramatic family scene creates an absurd contrast between heavy emotional subject matter and lighthearted math wordplay.
References
The square root of 2 was historically the first number proven to be irrational, a discovery attributed to the ancient Greek Pythagorean school. Legend has it that Hippasus, who revealed this truth, was punished (possibly drowned) by fellow Pythagoreans for upsetting their belief that all numbers could be expressed as ratios of whole numbers.