1What a fight actually needs
A germ has targets that defenders can recognize
You only need two ideas. Watch each one:
A germ carries targets
A germ carries many recognizable parts. We draw just one target, like a lock, to explore how recognition works.
Only one key fits
A key fitting a lock is our picture of recognition. In this toy, one key matches one target. Real germs have many targets, and many immune cells can recognize them.
2Two ways the fight can start
Hunt for the key vs grab it off the shelf
In our toy, a matching response can begin in two ways. Real immune cells recognize targets together; they do not literally try keys one by one.
Hunt from scratch
The body tries key after key, hunting for the one that fits — while the germ keeps multiplying.
Grab it off the shelf
It already found the matching key once and kept a stack ready — so it grabs it the instant the germ shows up.
3Your turn — be the body, find the key
Tap keys to hunt for the one that fits
A germ just invaded. Tap keys on the ring to test them one at a time — only one matches its face. But hurry: every wrong tap, the germ multiplies.
4Now race two bodies
A new target arrives after practice
The top model has no memory. The bottom model remembers a triangle target ▲. Now both meet a round target ●. All other rules are the same. These two target shapes have no overlap in our toy. Predict first, then compare the response traces.
Guess before you start the race
With triangle memory but a new round target, will the bottom model begin its matching response earlier than the top model?