diff --git a/src/animation/animationRules.cpp b/src/animation/animationRules.cpp
index 0ec2091..251d6ef 100644
--- a/src/animation/animationRules.cpp
+++ b/src/animation/animationRules.cpp
@@ -15,29 +15,34 @@ constexpr Shape G = Shape::G;
 constexpr Shape H = Shape::H;
 constexpr Shape X = Shape::X;
 
-Timeline<ShapeSet> animatePhone(optional<Phone> phone, centiseconds duration, centiseconds previousDuration) {
+ShapeRule::ShapeRule(const ShapeSet& regularShapes, const ShapeSet& alternativeShapes) :
+	regularShapes(regularShapes),
+	alternativeShapes(alternativeShapes)
+{}
+
+Timeline<ShapeRule> animatePhone(optional<Phone> phone, centiseconds duration, centiseconds previousDuration) {
 	// Returns a timeline with a single shape set
-	auto single = [duration](ShapeSet value) {
-		return Timeline<ShapeSet> { { 0_cs, duration, value } };
+	auto single = [duration](ShapeRule value) {
+		return Timeline<ShapeRule> {{0_cs, duration, value}};
 	};
 
 	// Returns a timeline with two shape sets, timed as a diphthong
-	auto diphthong = [duration](ShapeSet first, ShapeSet second) {
+	auto diphthong = [duration](ShapeRule first, ShapeRule second) {
 		centiseconds firstDuration = duration_cast<centiseconds>(duration * 0.6);
-		return Timeline<ShapeSet> {
-			{ 0_cs, firstDuration, first },
-			{ firstDuration, duration, second }
+		return Timeline<ShapeRule> {
+			{0_cs, firstDuration, first},
+			{firstDuration, duration, second}
 		};
 	};
 
 	// Returns a timeline with two shape sets, timed as a plosive
-	auto plosive = [duration, previousDuration](ShapeSet first, ShapeSet second) {
+	auto plosive = [duration, previousDuration](ShapeRule first, ShapeRule second) {
 		centiseconds minOcclusionDuration = 4_cs;
 		centiseconds maxOcclusionDuration = 12_cs;
 		centiseconds occlusionDuration = clamp(previousDuration / 2, minOcclusionDuration, maxOcclusionDuration);
-		return Timeline<ShapeSet> {
-			{ -occlusionDuration, 0_cs, first },
-			{ 0_cs, duration, second }
+		return Timeline<ShapeRule> {
+			{-occlusionDuration, 0_cs, first},
+			{0_cs, duration, second}
 		};
 	};
 
@@ -47,59 +52,59 @@ Timeline<ShapeSet> animatePhone(optional<Phone> phone, centiseconds duration, ce
 		return animatePhone(referencePhone, duration, previousDuration);
 	};
 
-	static const ShapeSet any = { A, B, C, D, E, F, G, H, X };
+	static const ShapeRule any{{A, B, C, D, E, F, G, H, X}};
 
 	if (!phone) {
-		return single({ X });
+		return single({{X}});
 	}
 
 	switch (*phone) {
-	case Phone::AO:			return single({ E });
-	case Phone::AA:			return single({ D });
-	case Phone::IY:			return single({ B });
-	case Phone::UW:			return single({ F });
-	case Phone::EH:			return duration < 20_cs ? single({ C }) : single({ D });
-	case Phone::IH:			return single({ B });
-	case Phone::UH:			return single({ F });
-	case Phone::AH:			return single({ C });
-	case Phone::Schwa:		return single({ { B, C, D, E, F } });
-	case Phone::AE:			return single({ C });
-	case Phone::EY:			return diphthong({ C }, { B });
-	case Phone::AY:			return duration < 20_cs ? diphthong({ C }, { B }) : diphthong({ D }, { B });
-	case Phone::OW:			return single({ F });
-	case Phone::AW:			return duration < 20_cs ? diphthong({ C }, { F }) : diphthong({ D }, { F });
-	case Phone::OY:			return diphthong({ F }, { B });
-	case Phone::ER:			return duration < 7_cs ? like(Phone::Schwa) : single({ F });
+	case Phone::AO:			return single({{E}});
+	case Phone::AA:			return single({{D}});
+	case Phone::IY:			return single({{B}, {C}});
+	case Phone::UW:			return single({{F}});
+	case Phone::EH:			return duration < 20_cs ? single({{C}}) : single({{D}});
+	case Phone::IH:			return single({{B}, {C}});
+	case Phone::UH:			return single({{F}});
+	case Phone::AH:			return single({{C}});
+	case Phone::Schwa:		return single({{B, C, D, E, F}});
+	case Phone::AE:			return single({{C}});
+	case Phone::EY:			return diphthong({{C}}, {{B}, {C}});
+	case Phone::AY:			return duration < 20_cs ? diphthong({{C}}, {{B}, {C}}) : diphthong({{D}}, {{B}, {C}});
+	case Phone::OW:			return single({{F}});
+	case Phone::AW:			return duration < 20_cs ? diphthong({{C}}, {{F}}) : diphthong({{D}}, {{F}});
+	case Phone::OY:			return diphthong({{F}}, {{B}, {C}});
+	case Phone::ER:			return duration < 7_cs ? like(Phone::Schwa) : single({{F}});
 
 	case Phone::P:
-	case Phone::B:			return plosive({ A }, any);
+	case Phone::B:			return plosive({{A}}, any);
 	case Phone::T:
-	case Phone::D:			return plosive({ B, C, F, G, H }, any);
+	case Phone::D:			return plosive({{B, C, F, G, H}}, any);
 	case Phone::K:
-	case Phone::G:			return plosive({ B, C, E, F, G, H }, any);
+	case Phone::G:			return plosive({{B, C, E, F, G, H}}, any);
 	case Phone::CH:
-	case Phone::JH:			return single({ B, F });
+	case Phone::JH:			return single({{B, F}});
 	case Phone::F:
-	case Phone::V:			return single({ G });
+	case Phone::V:			return single({{G}});
 	case Phone::TH:
 	case Phone::DH:
 	case Phone::S:
 	case Phone::Z:
 	case Phone::SH:
-	case Phone::ZH:			return single({ B, F });
+	case Phone::ZH:			return single({{B, F}});
 	case Phone::HH:			return single(any);
-	case Phone::M:			return single({ A });
-	case Phone::N:			return single({ B, C, F, G, H });
-	case Phone::NG:			return single({ B, C, E, F, G });
-	case Phone::L:			return duration < 20_cs ? single({ B, C, D, E, F, G, H }) : single({ H });
-	case Phone::R:			return single({ B, C, E, F });
-	case Phone::Y:			return single({ B, C, F });
-	case Phone::W:			return single({ F });
+	case Phone::M:			return single({{A}});
+	case Phone::N:			return single({{B, C, F, G, H}});
+	case Phone::NG:			return single({{B, C, E, F, G}});
+	case Phone::L:			return duration < 20_cs ? single({{B, C, D, E, F, G, H}}) : single({{H}});
+	case Phone::R:			return single({{B, C, E, F}});
+	case Phone::Y:			return single({{B, C, F}});
+	case Phone::W:			return single({{F}});
 
 	case Phone::Breath:
 	case Phone::Cough:
-	case Phone::Smack:		return single({ C });
-	case Phone::Noise:		return single({ B });
+	case Phone::Smack:		return single({{C}});
+	case Phone::Noise:		return single({{B}});
 
 	default:				throw std::invalid_argument("Unexpected phone.");
 	}
diff --git a/src/animation/animationRules.h b/src/animation/animationRules.h
index e21bb74..4b86119 100644
--- a/src/animation/animationRules.h
+++ b/src/animation/animationRules.h
@@ -9,4 +9,11 @@
 // A set of mouth shapes that can be used to represent a certain sound
 using ShapeSet = std::set<Shape>;
 
-Timeline<ShapeSet> animatePhone(boost::optional<Phone> phone, centiseconds duration, centiseconds previousDuration);
+struct ShapeRule {
+	ShapeRule(const ShapeSet& regularShapes, const ShapeSet& alternativeShapes = {});
+
+	ShapeSet regularShapes;
+	ShapeSet alternativeShapes;
+};
+
+Timeline<ShapeRule> animatePhone(boost::optional<Phone> phone, centiseconds duration, centiseconds previousDuration);