Took a couple of dogs caving with me... one of them tried to swim up a falling lava stream, after I'd already quenched the base – there was plenty of room.  "Dog tried to swim in lava" – yep, they sure did!  The other wandered across the corner of a half-quenched lava pool, and burned to death, and had no obvious reason to want to go down that corridor.

This is actually in 20w17a, since my launcher doesn't seem to see 20w18a