Explain SMBC — the wiki for Saturday Morning Breakfast Cereal

The Joke

A person is talking to Jesus (depicted with a halo) and is surprised to learn that when Jesus bleeds, his blood turns into alcohol. Jesus sheepishly confirms this. The person then immediately tells Jesus: "I need you to stand in my yard for 48 hours." The caption below reads: "Jesus made an excellent mosquito trap."

The joke combines two ideas. First, there is the Christian doctrine of transubstantiation, which holds that during the Eucharist, bread and wine become the literal body and blood of Christ. The comic inverts this: if wine is the blood of Christ, then the blood of Christ is wine (i.e., alcohol). Second, the comic applies this to a practical problem -- mosquito traps often use carbon dioxide or fermented substances to attract mosquitoes. If Jesus is standing in a yard and his blood is literally alcohol, mosquitoes would be attracted to bite him and then be effectively intoxicated or trapped.

The Humor

The humor comes from the absurd but internally logical application of a theological concept to a mundane household problem. The person is not awed by the miraculous nature of Jesus's blood turning into alcohol -- instead, they immediately see a practical use for it as a mosquito trap. The deadpan pragmatism of the request ("stand in my yard for 48 hours") contrasts hilariously with the sacred nature of the miracle being exploited.

References

Transubstantiation is a doctrine in Catholic theology that holds that during the Eucharist, the bread and wine literally become the body and blood of Jesus Christ, while retaining the outward appearance (or "accidents") of bread and wine. The comic plays on the reverse implication: if wine becomes blood during the Eucharist, then perhaps Christ's actual blood has wine-like (alcoholic) properties.