Two of my erasers fused together

They seem to be made of different kinds of material each, the larger one being harder and more consistent. The pink one stuck to it and has since been "melting" (it's been about one year). What is the chemical explanation for this?

They seem to be made of different kinds of material each, the larger one being harder and more consistent. The pink one stuck to it and has since been "melting" (it's been about one year). What is the chemical explanation for this?