Deliberate mistake: There was no possible way for Edith to still be alive after the spiked coffin closed in on her. There are spikes on the doors and at the very back and sides of it, and she couldn't have squeezed in to brace herself. Probably done for obvious reasons, but still a mistake nonetheless.
Other mistake: While Gru is shrinking the moon the camera revolves quickly around the moon as it shrinks. When it cuts to the minions watching from earth, they have the same perspective as us.
Chosen answer: It is not very difficult to hold a straw between one's teeth, or gums and speak at the same time. A coworker of mine does it all the time with a pen.
MasterOfAll