Title text: The one time I tried, I got hit by a slinky going down at double speed.
This comic shows two simple line graphs on the same chart. One shows society's expectations, the other what Randall actually felt. The visual joke is that the societal expectation graph is treated like an actual down-moving escalator, with people on it.
An escalator is a continuously moving mechanized stairway that travels in a particular direction, either up or down. Traditionally, people stop walking when riding the escalator, and simply stand (perhaps holding the hand-rail) until they reach the destination and then step off. However, if you are in a hurry or impatient, it is possible to also climb the stairs manually, increasing your effective speed of ascent or descent.
Young children are typically fascinated by escalators, and will often want to run up and down them just for fun. A variation is to travel the escalators in the opposite to the intended direction. Running up the down escalator is type of physical challenge, especially for younger children, as they are fighting gravity and the downward motion of the escalator to reach the top. If they pause or cannot keep up sufficient speed, the escalator will impersonally return them to their starting position.
The curved graph on the chart shows how the urge to run up the down escalator is expected to peak at about age 7 and then decline steeply as you approach adulthood, although never quite reaching zero. For Randall (it seems to be Randall who is speaking), the urge has not diminished in any way, and even seems to be showing an upward trend as the graph approaches 24 years of age.
He does not appear to have acted upon this urge very often; in fact he claims only once.
The title text refers to the Slinky toy, a coiled spring that is designed to go down stairs by itself in an amusing manner. Since the Slinky is moving with the flow, its effective speed is doubled. A normal Slinky is very small and would not be able to halt an average human being through its inertia, but it could tangle up in their feet or otherwise trip them up, and would at least be a surprising encounter.
- [Graph with y axis titled "Urge to try running up the down escalator", with "weak" by the bottom and "strong" by the top. x axis has every two years labeled and every year signified by a smaller mark, which stops at 24. A red line with "What I was supposed to feel" with points at every line rises, peaks at 7 years old, then falls "tangent graph" shaped until the end. Along this line are shown various stick-figures at 12, 14, 20 and 24. A second red line runs "What I've actually felt" which stays consistently high.]