I’m pretty sure an ace lead is the SECOND best in the match. The trump card is decided before the match and is more powerful unless it isn’t there. Therefore, trumping an ace lead is pretty devastating to the person with the ace lead.
The joke was that Mister Magoo confused Heathcliff for Garfield (they look similar from the front and both walk on 2 legs). Apparently, Mister Magoo and Elmer Fudd are also confusable so @monkeysky was joking about doing the same thing Mister Magoo did (confuse ppl/cats).
Not sure actually it’s my best guess.