Beamed directly into your brain by: bill33
The author writes:
Here's something funny I learned today called a "double entendre": The sentence "I helped my uncle Jack off a horse", when spoken, can be interpreted to mean helping your uncle Jack dismount a horse, or helping your uncle Jack kill a horse. This is funny not only because the preposition "off" is being used improperly, but because the word as a preposition is confused with the word as a verb! Ha ha ha!
Anyway, Tim's currently engaged in a rather family-unfriendly activity, as implied by the last panel of the previous comic, which is why he isn't shown here.