[garrettgrimsley]

For any still not seeing it: The chain stay from the bottom bracket is missing. The rear wheel should be held by a triangular arrangement of the frame, but the side of the triangle that runs parallel to the ground isn’t there

[bena]

I didn't want to mention what I thought was wrong because I didn't want to accidentally influence anybody else, especially if I wound up wrong.

But yeah, after giving it a good, long look, along with his mention that it would break when someone sat on it, I guessed that there should have been a bar between the back wheel and where the pedals are.

[skykooler]

I'm not sure it would break when you sat on it; the chain would be in tension, holding those two sections together and filling the task of that bar. The problem would be when you started to pedal, and that bar is not there to stop the chain from pulling the rear wheel towards the pedals.

[logfromblammo]

That isn't the only thing wrong. If you brace the back wheel, the fore tube still has a single point of attachment, and the front wheel would tend to flex forward, encouraging the weld between the rising forward diagonal of the triangle and the fore tube to break.

It might not break right when someone sat on it, but after stresses accumulate from riding over bumps, the front portion is going to break off and pitch the rider forward into the pavement.

[gascan]

Finding that particular omission just feels like visual trickery, rather than anything to do with knowing how a bike works.

Like any number of puzzle books that include a "find the missing X!" and friends.

[jshevek]

Yes, it took me a moment to identify the omission because the chain itself occupies nearly the same space

[komali2]

After googling bicycles, seems to me like the common shape is "diamond with a line dividing the two triangles (bicycle seat thingy) and a line coming off the top vertex (front wheel holder thingy), I'm gonna try to remember that and draw a bicycle later after the memory has faded.

[sampo]

The single joint between the down tube and the head tube is probably not mechanically very strong, either.

[Johnythree]

Plus the front forks are straight.

eg they have "Rake", but no offset, so the amount of "Trail" or "Castor" will be incorrect.

https://en.wikipedia.org/wiki/Bicycle_and_motorcycle_geometr...

[Yaggo]

It's called a fork, not forks.

https://en.wikipedia.org/wiki/Bicycle_fork