What is this red stuff inside my bananas?

Lately I’ve noticed some kind of reddish bruise in some of my bananas. Not ON them, like a regular bruise, but under the surface, with no mark on the peel. You can barely see it looking at the peeled banana, but if you scrape off the top layer with a thumbnail, there is a reddish bruise under the surface. And sometimes if you split it down the middle, you can see that it has infiltrated the core for a significant portion of the length.

It stands to reason that some of these “bruises” are too deep inside to see from the outside, so I’ve probably eaten many bananas like this without noticing them. So I know it’s not something lethal, but I still don’t want it in my bananas.

Can anyone tell me what it is, and whether there is any way to detect it before peeling, i.e. in the store before I buy?