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What's that? You're not into astrophysics or particle physics? Well, allow me to enlighten you.
Currently, in France and Switzerland, there's a giant machine called the LHC, run by an organization called CERN. Some people are afraid that, when this machine is switched on, it will cause the end of life on Earth. The aliens in the first 2 panels have created a similar machine (that's the CERN logo in the upper right), and when they turned it on, it created a gamma ray burst. The alien in panel 2 is pushing a button with his tentacle-fingers, not trying to open a can of tuna with a wrinkled bow tie.
A gamma ray burst is an explosion that makes a supernova look like one of those popper-snapper firecrackers that you can set off in your hand. No-one is sure what causes them, but they're thought to be caused by things like collisions between black holes. (Technically collisions between neutron stars, which are sort of almost-black-hole things.)
So, yeah... the joke is that gamma ray bursts are actually caused by civilizations reaching this particular phase of development, then nuking themselves to smithereens by accidentally building a doomsday machine.