system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: why does wasabi heat affect our noses while chili pepper heat affect our tongues?
gpt
It comes back to different chemicals that are present in these different foods.  The pungent chemical present in chili peppers, capsaicin, excites our tongue and triggers similar reactions that a high temperature would cause, so we associate it very directly with "heat."  Other chemicals like piperine (found in many peppercorns) have similar effects, though most people find piperine to be more biting and less hot.

With wasabi, as well as horseradish, mustard, and a few others, the chemical that gives it its pungency is allyl isothiocyanate, which our body reacts to a little differently and which has a stronger effect on our sinuses - as anyone who's taken too big a bite of horseradish or wasabi can tell you, they can cause a pretty major reaction.  It can actually be great if you need to clear your sinuses too!

Both chemicals ultimately have the same goal - the plants want to avoid certain animals eating them as much as possible - they just work in slightly different, convergent ways.  The effect of these chemicals repels most mammals and insects, while birds, who aren't as affected, will happily eat chili peppers and spread their seeds.  Humans, being the crazy things that we are, have decided that we enjoy these sensations in moderation, and we've found ways to incorporate them deliciously into food.  And there are others as well - the piquancy of ginger and garlic, the numbing heat of szeschuan peppers, these are all different chemicals that make our food flavorful and interesting in different ways.