Counterfactual thinking and the origin of language
This is controversial, to say the least, and possibly false according to one interpretation on such experiments with monkeys. But note that there is a subtlety here: the way counterfactuals are usually tested with monkeys involves them having seen what a reward could have been, but had not received.

Recent studies on reinforcement learning in primates indicate that humans are not alone in
our ability to think about hypothetical outcomes. For example, Lee and colleagues (Abe &amp; Lee
2011, Lee et al. 2005) presented rhesus monkeys with a computer-based version of the game rock-
paper-scissors. When they examined the strategies that the monkeys used over time, they found
that monkeys did not simply adjust their choices based on what they received on the previous trial.
Surprisingly, monkeys also adjusted their strategy to account for rewards they would have received
had they chosen a different option. Using a similar computer-based setup, Hayden and colleagues
(2009) presented rhesus monkeys with a risky decision-making task with eight possible choices.
Whereas seven of the options consistently provided small juice rewards, the final option was
variable: Sometimes it provided a much larger reward, and sometimes it provided a much smaller
reward. Critically, monkeys were given feedback about what the risky option would have provided
on every trial. In this way, monkeys could see how much juice they would have gotten from the
risky option, regardless of whether they had chosen it. As in the rock-paper-scissors task, modeling
of the monkeys’ behaviors showed that the monkeys adjusted their future strategies on the basis of
what they would have received. In cases where the risky option would have provided the high-value
outcome on one trial, monkeys were especially likely to seek this option out in future trials. In this
way, monkeys—like humans—change their future choices according to counterfactual situations
that could have (but did not) happen.

(There's subsequent para that discusses that monkeys, like us, seem to be driven by regret-like emotional responses in such matters.)
More recent experiments indicate that monkeys intentionally explore the &quot;counterfactual space&quot;, i.e. try to find out what rewards they might have missed, even if they aren't just shown these potential rewards without them incurring an actual cost (in terms of missing other rewards, already known to them). Rather unsurprisingly, monkeys are willing to pay, in terms of missing certain rewards for finding out &quot;what else is there&quot;, i.e. they (&quot;deliberately&quot;) pay for information.
I think Chomsky isn't really talking about this though; actually he's not even using &quot;counterfactual&quot; in the para you cited but &quot;minds capable of envisioning that the world could be otherwise than it is at this moment&quot;. Basically: do the monkeys merely think of the world in a seen-potential-reward and seeking-information-about-unknown-rewards fashion, or do they &quot;truly imagine&quot; there could be rewards they didn't ever see? That's probably (very) difficult to test. Basically, his thesis/question isn't really about counterfactual thinking, but whether monkeys &quot;have imagination&quot; in some kind of &quot;visual language&quot; perhaps...