When Wiggum has his chest marked by El Barto and falls on his face, he has an open eye in front of a closed eye.
Tomatoes were not introduced into Italy until near the end of Leonardo's life and did not become popular for about 200 years. Lisanardo's mother would not be making tomato sauce.
Toulouse-Moetrec is seen in 1863, however Henri de Toulouse-Lautrec was born in 1864.
In order to set up a joke about how easy guillotines are to use, Principal Skinner claims that in France the guillotine "... hasn't been used for years. No-one even remembers how to work it!" In fact the guillotine never fell into disuse, from the French Revolution right through to the abolition of the death penalty in 1977.