How painkiller pill would know where the pain in the body??

In fact they wouldn't!!..then do they act blindly??
Actually damaged body cells produces a large amount of enzyme 'cyclooxygenase', which acts on cell membrane and leads to the formation of prostaglandins(hormone like substances), which in turn send pain signals to the brain; additionally swelling, redness are also mediated by them -- Pain

Painkiller Pill -- aspirin like drugs when taken, enters into the blood stream, travels all over the body and where the level of the enzyme cyclooxygenase is high, it binds to it and prevents its functions;
So No prostaglandins produces > No pain > No pain signal to nerves system.

         But pain isn’t always bad, even if it doesn’t feel very good. Pain is our body’s way of warning of something is wrong so we could fix it. If we didn’t feel pain, we might not realize that there was a problem, and it could get much worse before we notice it.

...and little about painkillers.. broadly they are of 2 types:
type 1 - they don’t remove the pain. Instead they act on the pathway which sends pain signals to the brain and also in the brain to alter the perception of the pain;Steroidal
type 2- actually removes the pain itself; which we take over the counter/ medical shop; Non Steroidal

disclaimer - terms/ biological short answers used may not be 100%, roughly 20 mins of googled knowledge, hence limited understanding.

PS: may be should stick to type 1, do you?

What does the number(within triangle recycle logo) on plastic bottle or cover mean?

It was a work from home day for me, and it was after noon lengthy call and my presence required was least, so left with option - be on mute; I leave it your imagination to guess how WFH productive would it be especially post lunch! as usual look over thing on the table..rolling the water bottle...come across the glancing the description found on bottle bottom... recycle icon(triangular chasing arrows).. that's where I become attentive of googling about that...

Have you ever wondered of small triangle & a number within, mainly located on the bottom of plastic container or bottle, luckily cover doesn't have one! I meant bottom not the number, hence easily noticeable. Need not to worry even if we haven't as the purpose of it is for composite identity & recyclable nature. In other words,

• How to recycle that specific plastic
• How toxic that plastic is
• What should be or not be inside that container,

which is really bigger picture, still pretty table at the bottom here may give kick start, if interested. With the intent of day to day consumption basis, let me touch base 3rd point(Health) and leave the rest(environmental) for your interest.

and the term BPA?... I'm sure you have heard.... developed cities takes about it much nowadays!
Plastic water bottles are made from polyethylene terephthalate. For either of the reason below, it could releases the toxic chemicals antimony and bisphenol A, commonly called BPA. Which is off-course harmful, BUT depends on the level it get mixed and I'd not flag as 1 category and confuse here.

Acceptable we do can't gave up, but try let's compromise with time/money rather health. With that said, just 2 thing to note.

1. One Time Use - #1 mostly found on water bottles which can't be avoided and it's safe too unless kept in high temperature.

2. Re-Use(Reduce Reuse) - Going with #5 or "PP"(Poly Propylene) printed ones, when it comes to re-use as both safe, and very economical to use with the only caveat being that it may not be as pretty and clear/transparent as your PET bottle.

FYI -

Why alphabets in toll free number?

        Randy's Wooster pizza shop in Manchester, right next to Tolland-Buckland junction, their fancy Red lightened toll free number(just similar to "OPEN" sign board on restaurant glass door) would easily catches one's eye while waiting in junction for traffic signal to GREEN, Perhaps they wanted encourage take away and hence their contact number was eye catchy than shop name font. In fact I just googled it prior to this write up as even I couldn't recall that pizza shop name though have glanced that at least 20 times!

        Their contact number was something like 'CALL 666 NOW', to be honest with you I had no clues until I saw 1 800-CALL DHL printed on their big courier vehicle some other day. That's the spark, I just saw CALL DHL with well known hotline prefix 1800, and not the 1 800 225 5345, wow how cool was that? friendly name like brand rather series of number, though whatever fancy that be. Each letter in the alphabet corresponds to a number on a number pad. ABC - 2, DEF - 3, GHI - 4, JKL - 5, MNO -6, PQRS - 7, TUV - 8, WXYZ - 9. Most number pads on phones probably show which characters correspond to each number.

Necessity is the mother of invention, heard? History repeats, heard too? have you ever had guess, it was there in black & white generation too! ha ha