I'm not sure to which story you are referring, but here's what the symbols mean. A pendulum is the part of a clock (i.e. a grandfather clock) that counts the seconds as they pass. They would symbolize the unstoppable nature of time. An old man with a scythe might represent the grim reaper or another figure of death.
Both of these symbols have to do with growing older and moving on (dying).
Hope this helps! :)
He read his textbooks carefully and made concept maps to help him remember the details.
