Arthur C. Clarke's "Castaway" (short story, science fiction): Just looking at an alien could kill it!
One of the more imaginative alien designs. Not only can recognizing an entity as alien be tough, even attempts to recognize it as something alive can have unforeseen consequences!
Story summary.An unnamed but not very intelligent conscious being is caught in a storm. He is composed of ions & lives inside the Sun! This massive storm has now thrown him so high, he cannot get back to his solar home. The pressure of sunlight is throwing him away - to coldest reaches of space.
On this journey, he is caught by earth's magnetic field. He goes down, & settles somewhere on the surface Atlantic ocean.
At a later date - I don't recall if there is a mention of how much time has lapsed - there is a human trans-Atlantic aircraft passing by. Edward Lindsey on board observes curious & unnatural patterns below. He will show it to Sub-Lieutenant Armstrong, a crew member of the aircraft. They will try examining it with radar. Unusual radiation of radar will kill the alien!
Reader is left with no doubt that alien is dead. Humans examining the phenomenon from aircraft are merely puzzled about the curious phenomenon.
Fact sheet."Castaway", short story, review
First published: "Fantasy", April 1947, under pseudonym Charles Willis.