Defying mortal fear, you raise your lasgun, utter scripture, and let hot las fly. It hits its mark, dead center in where you'd think its head would be. It stops and sniffs, or it looks like it is. The fleeing guardsman, temporarily taken aback by this apparent divine intervention, takes his chance and scrambles to where he saw the shot come from: you.
The ambling shape that is the fellow guardsman slowly comes into view, solidifying through the heavy fog. His face is frantic and full of fear, but a heady calm possesses you. The calm before the storm. The calm before death.
Behind the bloodied, muddied face of the guardsman, is a face words cannot describe. Reality is offended by its presence, and the air around it burns with defiance. A tingling sensation trickles through your fingertips. In a mixture of instinct, fate and chance, your arms outstretch and blast the thing away.
"No...." Your Curse is resurfacing. The Warp-suffused marsh seems to push out the psyker in you. The thing, stunned, looks at you with renewed ravenous hunger, now aware of your true nature. "No!"
Your hands eschew multi-hued flames once more, and the thing is wrapped in dancing fire. It retreats into the mist. The splash of footsteps echoes behind you: the guardsman you saved is running away.
If he told the others that you were an unsanctioned psyker, you'd be executed, or worse. You could end him, now and here, a simple shot to the back. Or you could let the Death World's fauna and flora take him. But would you risk that chance? Or would you risk your honor and soul by killing your comrade?