Also, was the mouse warm enough? 101-103F? As was already said, I have one (Choco) that sometimes eats immediately, out in the open, but other times likes me to put a black T-shirt over his feeding container.
The only time I've seen one pick up a mouse and then spit it out was Inez when I increased prey size and she didn't think she could handle it. I downsized the mouse right then, and she ate normally.
Nanci