diff --git a/packages/ludic.effects/queries.ludic b/packages/ludic.effects/queries.ludic
index 5ce998c2..65245069 100644
--- a/packages/ludic.effects/queries.ludic
+++ b/packages/ludic.effects/queries.ludic
@@ -38,10 +38,22 @@ export function effects_at(effects_st: EffectsState, i: int) -> Effect {
   return e
 }
 
-# the indices of the ones that have begun, for a read-out
+# the indices of the ones that have begun, for a read-out (a frame's read-out fills its own list)
 export function effects_live(effects_st: EffectsState) -> []int {
   let out = new []int
-  let all = ef_all(effects_st)
-  for i in 0 .. len(all) { if ef_live(all[i]) { push(out, i) } }
+  effects_live_into(effects_st, out)
   return out
 }
+
+export function effects_live_into(effects_st: EffectsState, out: []int) -> void {
+  List.clear(out)
+  let all = ef_all(effects_st)
+  for i in 0 .. len(all) { if ef_live(all[i]) { push(out, i) } }
+}
+
+export function effects_live_count(effects_st: EffectsState) -> int {
+  var n = 0
+  let all = ef_all(effects_st)
+  for i in 0 .. len(all) { if ef_live(all[i]) { n += 1 } }
+  return n
+}
diff --git a/packages/ludic.effects/tests/effects_test.ludic b/packages/ludic.effects/tests/effects_test.ludic
index d370e92d..cce617df 100644
--- a/packages/ludic.effects/tests/effects_test.ludic
+++ b/packages/ludic.effects/tests/effects_test.ludic
@@ -71,6 +71,11 @@ program EffectsTest {
     effects_add_after(effects_st, 20.0, LEGS, -5.0, 15.0, false, "Sugar crash")
     expect(effects_sum(effects_st, LEGS) == 8.0)
     expect_eq(len(effects_live(effects_st)), 1)
+    expect_eq(effects_live_count(effects_st), 1)
+    let kept = new []int
+    effects_live_into(effects_st, kept)
+    effects_live_into(effects_st, kept)
+    expect_eq(len(kept), 1)
     tick_minutes(25.0)
     expect(effects_sum(effects_st, LEGS) == -5.0)
     tick_minutes(20.0)
diff --git a/packages/ludic.hints/index.ludic b/packages/ludic.hints/index.ludic
index 95bf889e..630237f6 100644
--- a/packages/ludic.hints/index.ludic
+++ b/packages/ludic.hints/index.ludic
@@ -6,6 +6,7 @@ import "ludic.base"
 import "defs.ludic"
 import "port.ludic"
 import "rail.ludic"
+import "rail_into.ludic"
 import "card.ludic"
 import "mute.ludic"
 import "system.ludic"
diff --git a/packages/ludic.hints/rail_into.ludic b/packages/ludic.hints/rail_into.ludic
new file mode 100644
index 00000000..07adfae1
--- /dev/null
+++ b/packages/ludic.hints/rail_into.ludic
@@ -0,0 +1,7 @@
+# rail_into.ludic - the rail into a list the caller keeps: a HUD asks every frame, and a list made
+# each time is never given back
+export function hints_rail_into(hints_st: HintsState, out: []int) -> void {
+  List.clear(out)
+  if not HintsWorld.showing() { return }
+  for k in 0 .. hints_st.hn_n { push(out, hints_st.hn_top[k]) }
+}
diff --git a/packages/ludic.hints/tests/hints_test.ludic b/packages/ludic.hints/tests/hints_test.ludic
index 941a203f..a8642a6f 100644
--- a/packages/ludic.hints/tests/hints_test.ludic
+++ b/packages/ludic.hints/tests/hints_test.ludic
@@ -74,6 +74,11 @@ program HintsTest {
     hints_test_st.showing = true
     hints_sort(hints_st)
     expect_eq(len(hints_rail(hints_st)), 1)
+    let kept = new []int
+    hints_rail_into(hints_st, kept)
+    hints_rail_into(hints_st, kept)
+    expect_eq(len(kept), 1)
+    expect_eq(kept[0], hints_rail(hints_st)[0])
   }
 
   test "the key opens the picked chip, the arrows walk round, the key puts it down" (hints_st: mut HintsState, hints_test_st: mut HintsTestState) {