pugs -e 'say shift [1, 2, 3].shift'
        pugs -e 'say shift([1, 2, 3].shift)'
        pugs -e 'say shift([1, 2, 3]).shift'

do not ever return, but yet does not seem to chew up the CPU either.

Meanwhile, these examples:

        pugs -e 'say pop [1, 2, 3].pop'
        pugs -e 'say pop([1, 2, 3].pop)'
        pugs -e 'say pop([1, 2, 3]).pop'

all print '3'.

Just a weird one, I thought I would share it. I am not even sure it is
really a bug to be honest (other than the fact it does not seem to
return).

I don't see how those can be semantically valid, even if they parse.
I read them as shifting the return value of a shift, which would
be an attempt to shift on a scalar.

: Meanwhile, these examples:
:
:       pugs -e 'say pop [1, 2, 3].pop'
:       pugs -e 'say pop([1, 2, 3].pop)'
:       pugs -e 'say pop([1, 2, 3]).pop'
:
: all print '3'.

Same problem.  3.pop doesn't mean much.  All I can figure is that
it's following the list-in-scalar context rule to make [3].pop
out of it.