You cover shrimp with ice to exhaust it. The ice makes the shrimp really tired. Give them enough ice, and they will soon become exhausted.
After you exhaust the shrimp, you put some ice on your jeans (じん) to cool yourself down. Exhausting the shrimp exhausted you as well, and you’re really warm from all that work you just did so you put some ice in and on your jeans to cool down a bit.
Currently there are no similar looking kanji which exist in the WaniKani learning system