The sign on the desk of Dr. Silverstein, Jack Brooks' shrink, misspells "counselor" as "councilor". (Despite various international spellings, a "councilor" is still someone who works for the council, and a "counselor" is someone who counsels.)
The "sodium" the teacher shows is actually dry ice.
When Jack is loosening the union on the pump, he is using the wrench on the wrong part.