Test screening viewers note that Crabbe and Goyle have little screen time and are never seen transformed as girls.
According to a source on IMDB, there will be a scene where Malfoy is testing the Vanishing Cabinet by putting apples inside it. This has either been changed or Malfoy will test it with Birds as well, due to info from the TLC Set Report.
Draco spending time in the Room of Requirement, sending birds through the Vanishing Cabinet as practice.
A calendar picture and a sticker book picture of Malfoy and a bird have both emerged.
A promotional picture shows Malfoy testing the cabinet.
A test screening viewer discusses the birds Malfoy uses.
Throughout the movie we keep seeing Draco going to a cage full of birds, like the one he has in his hand. He would would take one and then go off to the RoR. Later in the movie, I believe just before the Sectum Sempra Scene, we see him put one of the birds into the Vanishing Cabinet looking hopeful and closes it. When he opens it, the bird is dead.
Though we, as the audience are not really supposed to know what Draco is doing, his reaction to the bird being dead makes it obvious that whatever he is trying to do with that cabinet is not working. He is so upset that he ends up in the bathroom crying. And the Sectum Sempra scene takes place.
Rachel: Draco was going around with -- throughout the whole movie you keep seeing him get -- go to this cage of birds somewhere in the castle and he keeps taking one out so every time you see the cage it has one less bird in it. And so --
Rachel: -- and then -- and he takes the bird and -- to the Room of Requirement and -- and puts it into the cabinet. You only see him do it once, but you -- you see him take the birds many times. But --
Vince: So they all die? All the birds die?
Rachel: Well -- well, you can assume that they did. Except for probably the last one when he finally --
Scott: Yikes. (laughs)
Rachel: -- makes the cabinet work.
Vince: That's just awful.
Meesha: Where does he get the birds?
Rachel: That's a good question. It was -- I don't know if that was supposed to be in McGonagall's room or if it was --
Vince: That's what we were thinking.
Rachel: -- just some random place in the castle, but he was getting them from somewhere in the castle. There was a cage of birds there.
Meesha: So he didn't actually walk in through the gates carrying a cage of birds.