[alkh]

I am surprised that this is working, as I always thought that variables get initialized after the full command is parsed. So, I would assume that $_ would be related to the previous command (defined by a new line) and not this one, because there's no newline character here, but only an ampersand.

[godelski]

&& means there's a sequence. So the second statement will only execute conditioned on the first sequence. So...

  > thisFunctionFails && echo "Hello world" && echo "I SAID $_"
  
  > thisFunctionSucceeds && echo "Hello world" && echo "I SAID $_"
  Hello World
  I SAID Hello World

The left function has to get evaluated before the next function. So it is still related to the previous command.