The “trolley problem” is one of the most famous thought experiments in philosophy. In the classic version of the problem, a train is barreling down a track at five people. You’re in position to throw a switch, diverting the train to another track where it would only hit one person. So here’s your choice: Should you let the five people die, or make an active choice to kill the one person?

The basic idea is to test your feelings about killing versus letting die: whether intentions or outcomes matter. It’s generally used to help freshman philosophy students understand the difference between two major ethical theories, consequentialism and Kant-inspired deontology.

This 2-year-old doesn’t know about any of that. So when his father, psychology professor E.J. Masicampo, set up a trolley problem using a Thomas the Tank Engine toy, the boy solved it in a … pretty unique way:

“Uh oh,” indeed.

If you’re interested in reading more about the issues raised by the trolley problem, consequentialism, or deontology, go read the entries in the brilliant and reasonably accessible Stanford Encyclopedia of Philosophy (linked on each word). And if you’re interested in how the trolley problem does (or doesn’t) relate to real-life issues, go read my colleague Dave Roberts’s piece on the ethics of self-driving cars.