Depending on the actress and how it's done, that song the first time around also counts.
When you think about it, Seymour has never been loved in his life. He was abandoned at the Skid Row Home for Boys and subsequently taken out by a guy who hated him, made him sleep under the counter, and kept him around to do the work. Then he gets a magic plant, and suddenly Mushnik wants to be his dad! Audrey loves him! The world loves him! Everything's perfect...and then he's forced to go on a bloody, awful, evil killing spree, in part because he's afraid that if he gets rid of the plant, Audrey won't love him anymore.
Anyone who's seen Audrey's reprise of "Somewhere That's Green" as she dies in the director's cut knows that had it been left in the original theatrical version, she would have won an Oscar.
The musical build up to the dramatic chord actually makes this troper feel a bit of sympathy for Seymour, even if the whole situation's his fault.
It's even worse in the film than in the musical, for several reasons. Seymour had just proposed to Audrey, and they were about to elope together—she was in her wedding gown, for crying out loud! Plus, when Patrick Martin shows up afterwards, he finds Seymour standing at the top of a building, tears in his eyes, all ready to jump.
In fact, after the first take, Frank Oz told Ellen Greene that her performance was too restrained, and to let it all go. The next take was the last one.