Plug behind oil drain plug

[jerryt]

I acquired a 2008 gz 250 that has been sitting for three or four years, so before trying to start it I want to go through it to make everything right. I have a service manual on the way, but in draining the oil I pulled both plugs out of the bottom of the motor thinking they both may have to come out to drain all the oil. When I took the plug out that is toward the back of the motor a spring and some sort of a metal part came out. What is it and what does it do ? Can I just slide it back in there and put the plug back in?

Thanks