diff --git a/src/k_menu.h b/src/k_menu.h
index 33b08da0a..fb08ff4ab 100644
--- a/src/k_menu.h
+++ b/src/k_menu.h
@@ -1137,6 +1137,8 @@ void M_DrawAddons(void);
 #define CC_ANIM 3
 #define CC_MAX 4
 
+#define TILEFLIP_MAX 16
+
 // Keep track of some pause menu data for visual goodness.
 extern struct challengesmenu_s {
 
diff --git a/src/k_menudraw.c b/src/k_menudraw.c
index fc44aadde..5f5f69726 100644
--- a/src/k_menudraw.c
+++ b/src/k_menudraw.c
@@ -4518,7 +4518,7 @@ static void M_DrawChallengeTile(INT16 i, INT16 j, INT32 x, INT32 y, boolean hili
 	unlockable_t *ref = NULL;
 	patch_t *pat = missingpat;
 	UINT8 *colormap = NULL, *bgmap = NULL;
-	fixed_t siz;
+	fixed_t siz, accordion;
 	UINT8 id, num;
 	boolean unlockedyet;
 	boolean categoryside;
@@ -4569,14 +4569,26 @@ static void M_DrawChallengeTile(INT16 i, INT16 j, INT32 x, INT32 y, boolean hili
 		goto drawborder;
 	}
 
+	accordion = FRACUNIT;
+
+	if (challengesmenu.extradata[id].flip != 0
+		&& challengesmenu.extradata[id].flip != (TILEFLIP_MAX/2))
+	{
+		angle_t bad = (FixedAngle((fixed_t)(challengesmenu.extradata[id].flip) * (360*FRACUNIT/TILEFLIP_MAX)) >> ANGLETOFINESHIFT) & FINEMASK;
+		accordion = FINECOSINE(bad);
+		if (accordion < 0)
+			accordion = -accordion;
+	}
+
 	pat = W_CachePatchName(
 		(ref->majorunlock ? "UN_BORDB" : "UN_BORDA"),
 		PU_CACHE);
 
 	bgmap = R_GetTranslationColormap(TC_DEFAULT, SKINCOLOR_SILVER, GTC_MENUCACHE);
 
-	V_DrawFixedPatch(
-		x*FRACUNIT, y*FRACUNIT,
+	V_DrawStretchyFixedPatch(
+		(x*FRACUNIT) + (SHORT(pat->width)*(FRACUNIT-accordion)/2), y*FRACUNIT,
+		accordion,
 		FRACUNIT,
 		0, pat,
 		bgmap
@@ -4584,7 +4596,8 @@ static void M_DrawChallengeTile(INT16 i, INT16 j, INT32 x, INT32 y, boolean hili
 
 	pat = missingpat;
 
-	categoryside = !hili; // temporary
+	categoryside = (challengesmenu.extradata[id].flip <= TILEFLIP_MAX/4
+		|| challengesmenu.extradata[id].flip > (3*TILEFLIP_MAX)/4);
 
 	if (categoryside)
 	{
@@ -4725,8 +4738,9 @@ static void M_DrawChallengeTile(INT16 i, INT16 j, INT32 x, INT32 y, boolean hili
 		; // prevent div/0
 	else if (ref->majorunlock)
 	{
-		V_DrawFixedPatch(
-			(x + 5)*FRACUNIT, (y + 5)*FRACUNIT,
+		V_DrawStretchyFixedPatch(
+			((x + 5)*FRACUNIT) + (32*(FRACUNIT-accordion)/2), (y + 5)*FRACUNIT,
+			FixedDiv(32*accordion, siz),
 			FixedDiv(32 << FRACBITS, siz),
 			0, pat,
 			colormap
@@ -4734,8 +4748,9 @@ static void M_DrawChallengeTile(INT16 i, INT16 j, INT32 x, INT32 y, boolean hili
 	}
 	else
 	{
-		V_DrawFixedPatch(
-			(x + 2)*FRACUNIT, (y + 2)*FRACUNIT,
+		V_DrawStretchyFixedPatch(
+			((x + 2)*FRACUNIT) + (16*(FRACUNIT-accordion)/2), (y + 2)*FRACUNIT,
+			FixedDiv(16*accordion, siz),
 			FixedDiv(16 << FRACBITS, siz),
 			0, pat,
 			colormap
diff --git a/src/m_cond.h b/src/m_cond.h
index f8fa531d2..367f3d720 100644
--- a/src/m_cond.h
+++ b/src/m_cond.h
@@ -197,6 +197,7 @@ void M_PopulateChallengeGrid(void);
 struct challengegridextradata_t
 {
 	UINT8 flags;
+	UINT8 flip;
 };
 
 void M_UpdateChallengeGridExtraData(challengegridextradata_t *extradata);
diff --git a/src/menus/extras-challenges.c b/src/menus/extras-challenges.c
index fb8598eff..a9d056cd4 100644
--- a/src/menus/extras-challenges.c
+++ b/src/menus/extras-challenges.c
@@ -84,6 +84,16 @@ static void M_ChallengesAutoFocus(UINT8 unlockid, boolean fresh)
 		challengesmenu.col = challengesmenu.hilix = i/CHALLENGEGRIDHEIGHT;
 		challengesmenu.row = challengesmenu.hiliy = i%CHALLENGEGRIDHEIGHT;
 
+		// Begin animation
+		if (challengesmenu.extradata[i].flip == 0)
+		{
+			challengesmenu.extradata[i].flip =
+				(challengesmenu.pending
+					? (TILEFLIP_MAX/2)
+					: 1
+				);
+		}
+
 		if (fresh)
 		{
 			// We're just entering the menu. Immediately jump to the desired position...
@@ -261,7 +271,8 @@ void M_Challenges(INT32 choice)
 void M_ChallengesTick(void)
 {
 	const UINT8 pid = 0;
-	UINT8 i, newunlock = MAXUNLOCKABLES;
+	UINT16 i;
+	UINT8 newunlock = MAXUNLOCKABLES;
 
 	// Ticking
 	challengesmenu.ticker++;
@@ -275,6 +286,29 @@ void M_ChallengesTick(void)
 		challengesmenu.unlockcount[CC_ANIM]--;
 	M_CupSelectTick();
 
+	// Update tile flip state.
+	if (challengesmenu.extradata != NULL)
+	{
+		UINT16 id = (challengesmenu.hilix * CHALLENGEGRIDHEIGHT) + challengesmenu.hiliy;
+		boolean seeeveryone = M_MenuButtonHeld(pid, MBT_R);
+		boolean allthewaythrough;
+		UINT8 maxflip;
+		for (i = 0; i < (CHALLENGEGRIDHEIGHT * gamedata->challengegridwidth); i++)
+		{
+			allthewaythrough = (!seeeveryone && !challengesmenu.pending && i != id);
+			maxflip = ((seeeveryone || !allthewaythrough) ? (TILEFLIP_MAX/2) : TILEFLIP_MAX);
+			if ((seeeveryone || (challengesmenu.extradata[i].flip > 0))
+				&& (challengesmenu.extradata[i].flip != maxflip))
+			{
+				challengesmenu.extradata[i].flip++;
+				if (challengesmenu.extradata[i].flip >= TILEFLIP_MAX)
+				{
+					challengesmenu.extradata[i].flip = 0;
+				}
+			}
+		}
+	}
+
 	if (challengesmenu.pending)
 	{
 		// Pending mode.
@@ -594,8 +628,14 @@ boolean M_ChallengesInputs(INT32 ch)
 						challengesmenu.hilix = gamedata->challengegridwidth-1;
 					}
 				}
+
+				i = (challengesmenu.hilix * CHALLENGEGRIDHEIGHT) + challengesmenu.hiliy;
 			}
 
+			// Begin animation
+			if (challengesmenu.extradata[i].flip == 0)
+				challengesmenu.extradata[i].flip++;
+
 			return true;
 		}