What has slowed my Mac?

[iMore Question]

My primary concern is that I can't move about my(old--Snow Leopard--Mac) as quickly as I did a couple weeks ago. But where it shows most clearly is when I play solitaire(yes--my face is red). The card movement is not only much slower but shows a jerkyness as they move. Have I picked up a bug from the internet?--or added software that causes this?

 

[kch50428]

Any recently added apps? Updated apps? Do you leave a lot of apps running all the time?