People are only just finding out why biro lids have holes in them

One of life's great mysteries has finally been solved: why do biro lids have holes in them?

It's a question that has puzzled mankind since the dawn of time, but there is actually a very simple explanation.

While some people think it's to do with the flow of the ink, the real reason is actually much more important.

According to Bic, the hole is a key safety feature.

Pablo Paul/Alamy

The pen giant's website explains: "The reason that some BIC® pens have a hole in their cap is to prevent the cap from completely obstructing the airway if accidentally inhaled.

"This is requested by the international safety standards ISO11540, except for in cases where the cap is considered too large to be a choking hazard."

The vital piece of info was also shared on the Instagram page Zack Films.

In a post to his account, Zack explained that companies such as Bic are required to make sure their lids have holes in to protect customers.

In his video, Zack says: "You see, it's just enough space for airflow if the cap gets stuck in someone's throat.''

And for many people, it was the first time they'd heard about it.

One user said: "Never knew why. Thanks for sharing."

Some, however, weren't quite as impressed.

"Very old news," said one, while another commented: "Everyone knows this by now."

If that wasn't an information overload, we've got another one for you.

What's the deal with postal workers writing 'P' on letters all the time? It's very suspicious. Like a warning of some sort.

Well, not quite.

A collective of Reddit sleuths have been on the case, and have now revealed what it means.

One of the initial hypotheses suggested the 'P' indicated a home housing expensive pooches, so thieves (none specifically, just general thieves, thieves in general) would know where to go snooping.

Geoff Smith/Alamy

An undercover postie who had snuck into the Reddit forum could handle the guessing game no longer and stepped in with the surprise answer.

They said: “It's the postie's way of reminding themselves that when they come to post your letter there's also a parcel for you.

"That's so they don't post your letter then find out halfway down the street they forgot to knock and give you your parcel.

"Or sometimes they'll write P10 or something on the previous letter - that lets them know they have a parcel for next door (number 10) but no letter.”Very subtle Wordle clue - takes 5 days then you just rearrange them. Never right."

So, there you go, two mysteries solved in one day. What a way to end the week.