The usual reference is to bologna or salami. But with a more health-conscious generation, euphemisms are likely to evolve.I have heard countless euphemisms for the act, but this is the first tie I have heard it called "squeezing the spinach".
Frankly if a greenish hue is present it is time to contact a medical professional.
There are some jokes that come to mind about ripeness, but I too would recommend medical examination ASAP if such color was to occur.