What do Heathcliff and Catherine do at the Grange?

By the time we've reached Chapter 6 of Wuthering Heights, Heathcliff and Catherine are becoming increasingly rebellious, seeking sanctuary in nature from the vengeful Hindley and his silly wife. During one of their little adventures they wander over to Thrushcross Grange, home to the Linton family.
Heathcliff thinks it quite an impressive pile; although he does find the children who live there rather stupid. Indeed, he and Catherine think that the Lintons are such idiots that they openly laugh out loud at them. When they hear the sound of laughter, the Lintons realize that they have stalkers on the premises and set their vicious dog Skulker on what they probably think are a couple of burglars. As the two trespassers attempt their escape, the Lintons' mutt catches up with them and bites Catherine on the leg.