Finger Poke Test

"Scientific test number 1: Poke it."

- Gunnerkrigg Court

Is this thing real? Is that guy alive? Does a component sit in its slot well? Is the dough done? Does the icing for a cake have right consistency? Is this fish hook sharp en-OUGH!..

Every human being seems to instinctively know the default way to find the answers to any of the above questions and much more: poke the object of your doubts with a finger.

Of course, it's also the most common way to find out that the object is too hot, too cold, electrified, consists of flesh-melting goo, etc. Poking many other things is not directly dangerous, but still likely to land the intrepid explorers in hot water far out of their depth. And it's usually not the best way to find out "What Does This Button Do?"

See also Don't Touch It, You Idiot! for cases when it's an obviously bad idea, but someone does it anyway, Finger-Poke of Doom for cases when the catastrophic consequences are applied to the poked object and Giving Someone the Pointer Finger for social related behaviour.

Literature

 * In the horror novel Escardy Gap, one of the characters tries to poke the force wall surrounding the town only to have every part of his arm that went past the edge disappear. He consequently dies of blood loss.

Religion

 * The Bible. When the apostles struggled to believe their own eyes seeing their teacher resurrected, Thomas knew what to do.

Tabletop Games

 * The Player's Handbook in Dungeons & Dragons gives the price listing for a ten-foot-pole because finger-poking stuff in a trap-infested dungeon can be deadly, especially with an old-schoold Dungeon Master.
 * The infamously deadly old module The Tomb of Horrors features early on a sphere of annihilation that proved to be the single most player-killing dungeon feature in the module. Curious players tried to finger-poke the sphere or jumped headlong into the darkness. Some slightly less incautious players tried sword-poking and merely lost their expensive magic swords. Wise players only had their cheap ten-foot poles disintegrated.

Web Comics
"Prof.Kursk: And this is a weird alien artifact that apparently contains an infinitely large space in an infinitely small dot. We have no idea how to control it or what's inside that space. Lt. Michaels: Sounds almost like a singularity to me. Prof.Kursk: Sort of, only not really, and artificial. Lt. Midori: Awesome! (pokes the device) Lt. Michaels: Don't Touch It, You Idiot! (tries to stop him but only succeeds at getting close enough to be zapped too)"
 * Freefall has Sam examining fire in microgravity.
 * Gunnerkrigg Court had a moment when Coyote demonstrated how he can "pluck the Moon from the very sky!", holding it in his paw before Antimony. Who responds by poking the ball of pale light with a finger. This left a lasting impression - not only astronomers had to explain what happened, but later disturbed had some questions to ask in the Court.
 * Later Parley tried to touch the Coyote's tooth blade with a gloved finger, but Annie and Kat screamed at her "don't!".
 * Dangerously Chloe had an amusing moment when Teddy grasped the horns of a succubus with two fingers to emphasize his point... let's just say he was entirely unprepared for her reaction - and then, of course, he got slapped. Earlier on the same day he grasped an angel's wing (though that time trying to show it to the third party rather than to examine it) - so she got flustered and slapped him, with the same wing.
 * Walking City Paradox. [//www.deviantart.com/stupidyou3/art/Walking-City-Round-1-Dusted-part-3-of-16-499648821 When we first met him], his left arm is prosthetic, but right arm is mummy-wrapped for some reason. Then there's a flashback about arriving to the place (spoilers!) - "[//www.deviantart.com/zeurel/art/Walking-CIty-Round-4-Set-10-532224406 And this is the set where Paradox touches everything he shouldn't]". Short version: a crazy golem just chopped off (and possibly cauterized) the guy's left arm. He blasts the golem... then walks deeper into the city and proceeds to touch every single glowing thingy on his path with his right hand.
 * Ascension Chronicles goes [//ascensioncomic.com/comic/4-12-20-p1/ pretty much like this]:

Real Life

 * The finger poke test is common in cooking, though more often than not it's a bad idea -- unhygienic, limited to surface (unlike fork poke test), imprecise and/or just asking for local, but severe burns (especialy when hot fat or molten sugar is involved).