The pre-frontal cortex. This is where the nuclear warhead needs to be planted and programmed to detonate. Dropping the warhead in the right place turns out to be a pretty easy task, given that its location doesn't need to be particularly precise. Making sure it detonates is also surprisingly simple, particularly given the Troubleshooters' complete lack of experience with weapons of mass destruction.
Convincing the nuclear warhead's bot brain not to detonate within a few seconds, however, turns out to be a trickier task to accomplish.
'Detonate? Of course I can detonate! Let's play the countdown game! Three! Two! O—'
'No no no. We need you to detonate, bu—'
'It would be my pleasure! Three! Tw—'
'—but not straight away. How about counting down from a higher number?'
'Like three? I can do that! Thr—'
'No! No, try 3,000.'
'Can I count down in thousands?'
'No. Um, count down in halves.'
'Okay! 3,000! 1,500! 750!'
'Argh, it's like talking to a child!'