Frozen 

How can you ad-lib in an animated movie? When Josh Gad is involved, anything is possible. Gad was the voice actor for Olaf, the magical snowman in Frozen.  

At one point, Olaf is dancing around and an icicle pierces his body. Gad throws out the line “I’ve been impaled” after Olaf was actually impaled by an icicle. This deadpan delivery of the line was so perfect that the crew decided it had to be kept in.