This is associative learning.
The reactions of George and Ken are based on when they are startled. George will learn to associate his sister's crying with him being startled because it happens every time his sister cries.
Whereas Ken will not know when his sister will cry or when he will be startled by the crying so this has no affect on Ken.
Hence, crying will affect George but not Ken.
You can also spray easy-off oven cleaner but you have to wear gloves because it can burn your skin leave it for about 15 to 20 mins rinse it and bam your shower head is clean.