The main problem with this level is that often you run out of combinations (groups of blocks to click) before enough Pets have fallen
Try to make small matches of only two or three blocks (or use a blockbuster) to make them last
Only two Pets can be on the board at a time, so concentrate on getting them down and out so another can fall
Sometimes one will get stuck, so just work on the other until the virus multiplies, a pinwheel drops, or you earn a blockbuster to help the first Pet down
The next move after a Pet has been saved will cause another Pet to fall
If you can, choose where this Pet will fall by making room in a column for it
Try to keep the Pets moving in one or two columns that have less blocks in them
Make good use of the pinwheels to open Pets and remove blocks
If it's possible you can wait until there are two Pets on board and open them both with one pinwheel
Study the board between moves to make sure there are enough matches to last the game, choose your moves carefully, and if the board is too difficult, don't be afraid to just quit and try again!