Sally is kissing Humphrey outside the backyard fence and is pulling on his tie. They are interrupted by a kid and she lets go of his tie. But, in the next shot, she is pulling on his tie again.
When Humphrey is climbing down the mattress springs, you can see the wire holding him up.
When Humphrey takes a cigar while in Mr. Simpson's office, the cigar is already lit and smoking before Mr. Simpson lights it.
There is a deadbolt lock on the door to the steamship company's office, but there is no corresponding hardware (plate, bolt) on the edge of the door - as can be seen when Humphrey leaves in a hurry. This is a common shortcut taken by set carpenters.
When Sally and Humphrey are sprung into the air and hang on the wire you can see the wires that is holding Sally up.