Puree the pineapple and strawberry separately and transfer to liquid measuring cups with a spout. The spout makes it a lot easier to pour the purees. Have your popsicle mold and wooden sticks ready. Pour the strawberry puree first. Fill the mold about halfway. Then slowly add the pineapple puree. Because the pineapple puree is more dense than the strawberry, it will displace some of the strawberry puree creating that desired swirl/marble effect.