bun
Explanation
This comic plays on the double meaning of "buns" -- referring to both bread rolls and buttocks.
A mother and child are at what appears to be a park or outdoor setting. The child says "Oh my God Mommy, what are those bunnies doing?" The mother responds with something like "It may not look like it, but they're making babies." In the next panel, a professor-type figure is lecturing students about how "sometimes animals with growth increase the somatotropin beta subunit and GH-beta..." -- using dense scientific jargon to describe a biological process.
The joke operates by setting up what appears to be a "birds and the bees" scenario with the rabbits, then pivoting to an overly technical, clinical explanation that strips all the awkwardness from the situation by burying it under impenetrable scientific language. The contrast between the child's innocent question and the professor's incomprehensible jargon satirizes how adults handle uncomfortable biological topics -- either with euphemisms or by retreating into such dense technical language that the original question is effectively dodged.
The title "bun" reinforces the rabbit connection (bunnies/buns) while keeping the joke's setup ambiguous.