i would call it 'chew-toy'

Haha yeah that's a pretty apt name actually! I fully expected it to be dead. Couldn't quite believe it when I saw it sprouting new growth!

A jungle cactus of some kind? Rhipsalis maybe?

hylocereus undatus / dragon fruit?

Yes looks like dragon fruit to me! I'm just into growing these! Great find!

Looks like Epiphyllum ackermannii to me.

I grow epi ackermannii and it generally grow flat leaves only.

Looks like an orchid cactus cutting to me.

Here's what my pitaya looks like right now

{{gwi:569991}}

and here's some cuttings I took off my orchid cactus. The one in the middle particularly looks like a "chew toy" lol

{{gwi:569993}}

Looking at photos I can't decide if it's an orchid cactus or a dragon fruit!

Laura, Epiphyllum ackermannii often grows triangular sections. If you have not had any, can't explain it, but the ones here grow them every year.

The notches on the new growth of a Hylocereus do not have the long (relatively speaking) spines growing. Their spines start out small and never grow like the photo shows the new growth having.

your right Dz. And seeing the second photo it looks more like ackermannii.