. ▁Th rees ▁can ' t ▁be ▁disc arded , ▁except ▁as ▁your ▁final ▁disc ard ▁when ▁going ▁out ; ▁the ▁same ▁is ▁true ▁of ▁wild ▁cards . ▁If ▁the ▁disc ard ▁p ile ▁is ▁empty , ▁a ces ▁and ▁se vens ▁can ' t ▁be ▁disc arded . ▁It ▁is ▁possible ▁( though ▁very ▁unlikely ), ▁however , ▁to ▁be ▁in ▁a ▁situation ▁where ▁you ▁have ▁only ▁wild ▁cards , ▁or ▁only ▁a ces , ▁se vens ▁and ▁wild ▁cards ▁with ▁an ▁empty ▁disc ard ▁p ile . ▁In ▁this ▁case ▁you ▁may ▁make ▁such ▁a ▁disc ard ▁( aces ▁or ▁se vens ▁if ▁possible , ▁wild ▁cards ▁only ▁if ▁there ▁is ▁no ▁other ▁choice ▁- ▁never ▁a ▁three ▁under ▁any ▁circumstances ). ▁However , ▁an ▁oppon ent ▁may ▁challenge ▁the ▁leg ality ▁of ▁such ▁a ▁play , ▁in ▁which ▁case ▁you ▁must ▁show ▁the ▁oppon ent ▁your ▁hand ▁to ▁verify ▁that ▁the ▁play ▁was ▁in ▁fact ▁legal . ▁ ▁Both ▁red ▁and ▁black ▁th rees ▁may ▁be ▁played ▁to ▁the ▁table ▁as ▁red ▁th rees ▁can ▁in ▁" class ic " ▁can asta . ▁Un like ▁in ▁other ▁versions ▁of ▁can asta , ▁this ▁is ▁optional . ▁As ▁in ▁other ▁versions , ▁a ▁player ▁who ▁plays ▁a ▁three ▁draw s ▁a ▁replacement ▁card . ▁ ▁M eld ing ▁rules ▁ ▁M eld s ▁that ▁do ▁not ▁include ▁se vens ▁or ▁a ces ▁work ▁as ▁in ▁" class ic " ▁can asta , ▁except ▁that ▁such ▁m eld s ▁can ▁include ▁at