In the final scene Oliver is holding the mic in his right hand, but it disappears in the next shot.
Lester the doorman has told Oliver and Charles that Mabel and Oscar left heading west (towards the Hudson River). This makes sense since they are leaving the Upper West Side going to New Jersey via the George Washington Bridge. However, instead they all head east all the way across Manhattan, through Central Park, to the East Side, and then onto the FDR Drive along the East River. All in the opposite direction they should have gone. When they suddenly decide to go to Long Island instead, that was the route they were already on.
While mistletoe is a hemi-parasitic plant and slightly toxic, it doesn't singularly kill trees. Mistletoe seeds are spread by wildlife and affects stressed trees that are already declining due to disease and insects.