The yellow toward the bottom of the sac looks like there could be fat inside. Sebaceous cyst could be possible. Hamartomas are a type of tumor on the skin that is not malignant. Here is a little about those. https://www.merckvetmanual.com/inte...erview-of-tumors-of-the-skin-and-soft-tissues
Let us knowwhat you find or if you decide to let a vet check it.
Let us knowwhat you find or if you decide to let a vet check it.