I need to explain methyl isocyanate as an intermediate reaction (Bhopal disaster) during a presentation to a group of people, many of whom have not had much chemistry or biology, or none.

For example, consider this hypothetical stepwise reaction:
A + B → C + D

The reaction includes these elementary steps:
A + B → X*
X* → C + D
The chemical species X* is an intermediate.

Could someone give me a very basic example to explain this? Could be a cooking example or mixing a drink.

Thank you,

Judith