what do these two items have in common ?

True story
I, a biochemist, am working with a prof of physics (don't ask)
He takes me to the optics lab and points to a box the size of refridgerator and says

we are going to use that laser
NEVER EVER power it up without turning on the water and checking the water flow on this flowmeter

me: what if hte water stops ?
him: RUN

a few minutes later:
me: do I need eye protection ?
him: no, just don't look at the beam

a few days later, I am setting up an agarose gel, something DNA people do every day, and it uses a DC power supply 100V 0.25 amp

and the physics guy comes up to me, VERY serious, I mean, listen to me please serious, and he says

that power supply is very dangerous, you can easily kill yourself with it