In the opening of the show, ALF is showing Brian how to play "Skleen Ball" and the basket next to Brian is a round white laundry basket. After they cut back from the dialog a few moment later, the basket next to Brian is has been changed to a brown and rectangular shaped basket.
When the can of anchovies hits the painting, it does so about one third the way down and about a quarter the way in, on its right hand side, and hits the clouds. But when Kate has a look at the damage in the kitchen, she finds the tear further down the right hand side, in the landscape part on the edge of the road in the picture. When she takes it off the wall, and the back of the painting can be seen, there are no rips nor tears apparent in it, but once she gets it into the kitchen, one can see the damage only then.
When Trevor asks how old Willy is, thinking it is his birthday, Willy tells him he will be forty five in August. Now back when ALF bumped his head and became Wayne Schlagel, Willy told him at that time that he already was forty five. As an aside, Max Wright, who played Willy, was no older than 43 when he said that to "Wayne".