They're also covered in glands that secrete sticky saliva to maximize those areas of contact.

舌头上还布满了分泌粘性唾液的腺体，最大限度地扩大接触面积。

To create a larger area of contact with the wall?

为了与墙壁形成更大的接触面积？

And the force of friction  does not depend on the size of the surface area of contact between the two surfaces.

并且摩擦力不取决于两个表面之间接触表面积的大小。