diff --git a/musicalgestures/_eulerian.py b/musicalgestures/_eulerian.py
index a6e6ef44..710355f5 100644
--- a/musicalgestures/_eulerian.py
+++ b/musicalgestures/_eulerian.py
@@ -169,8 +169,8 @@ def _open_writer():
         process = _open_reader()
         writer = _open_writer()
 
-        lowpass1 = None
-        lowpass2 = None
+        lowpass1: "list | None" = None
+        lowpass2: "list | None" = None
         # IIR cutoffs derived from the requested band
         r1 = freq_high * 2.0 / fps
         r2 = freq_low * 2.0 / fps
@@ -188,6 +188,8 @@ def _open_writer():
                 lowpass2 = [lvl.copy() for lvl in pyr]
                 filtered = [np.zeros_like(lvl) for lvl in pyr]
             else:
+                # built together on the first frame, above, and used together here
+                assert lowpass1 is not None and lowpass2 is not None
                 for k in range(len(pyr)):
                     lowpass1[k] = (1 - r1) * lowpass1[k] + r1 * pyr[k]
                     lowpass2[k] = (1 - r2) * lowpass2[k] + r2 * pyr[k]
diff --git a/musicalgestures/_flow.py b/musicalgestures/_flow.py
index 6bf02adc..92656c1e 100644
--- a/musicalgestures/_flow.py
+++ b/musicalgestures/_flow.py
@@ -183,6 +183,7 @@ def dense(
                 next_frame = cv2.cvtColor(cv2.resize(frame2, size), cv2.COLOR_BGR2GRAY)
 
                 if _use_gpu:
+                    assert farneback_gpu is not None  # created under the same flag above
                     gpu_next_frame.upload(next_frame)
                     gpu_flow_result = farneback_gpu.calc(gpu_prev_frame, gpu_next_frame, None)
                     flow = gpu_flow_result.download()
diff --git a/musicalgestures/_pose.py b/musicalgestures/_pose.py
index d5c0bd4e..2e347dd6 100644
--- a/musicalgestures/_pose.py
+++ b/musicalgestures/_pose.py
@@ -969,7 +969,10 @@ def mg_pose_waterfall(self: "musicalgestures.MgVideo", style: str = 'trajectorie
         overwrite=overwrite, style=style, connections=c.get('connections'),
         n_samples=n_samples, markers=markers, color_by=color_by, cmap=cmap,
         dpi=dpi, elev=elev, azim=azim, lw=lw, axes=axes, crop=crop)
-    self.pose_waterfall_figure = mgf
+    # a figure that could not be built is not a result: leaving the attribute
+    # absent keeps `hasattr` honest, where storing None would not
+    if mgf is not None:
+        self.pose_waterfall_figure = mgf
     return mgf
 
 
@@ -1014,7 +1017,10 @@ def mg_pose_segments(self: "musicalgestures.MgVideo", segments: list | None = No
         c['data'], c['names'], c.get('connections'), c['width'], c['height'], c['fps'],
         target_name, overwrite=overwrite, segments=segments, n_bins=n_bins, cmap=cmap,
         dpi=dpi, ncols=ncols)
-    self.pose_segments_figure = mgf
+    # a figure that could not be built is not a result: leaving the attribute
+    # absent keeps `hasattr` honest, where storing None would not
+    if mgf is not None:
+        self.pose_segments_figure = mgf
     return mgf
 
 
@@ -1065,7 +1071,10 @@ def mg_pose_center(self: "musicalgestures.MgVideo", save_data: bool = True, dpi:
             pd.DataFrame(cols).to_csv(os.path.splitext(target_name)[0] + '.csv', index=False)
         except Exception as e:
             print(f'Warning: could not save CSV: {e}')
-    self.pose_centered_figure = mgf
+    # a figure that could not be built is not a result: leaving the attribute
+    # absent keeps `hasattr` honest, where storing None would not
+    if mgf is not None:
+        self.pose_centered_figure = mgf
     return mgf
 
 
@@ -1103,7 +1112,10 @@ def mg_pose_distance(self: "musicalgestures.MgVideo", dpi: int = 200, target_nam
 
     mgf = render_pose_distance(c['data'], c['names'], c['width'], c['height'], c['fps'],
                                target_name, overwrite=overwrite, dpi=dpi)
-    self.pose_distance_figure = mgf
+    # a figure that could not be built is not a result: leaving the attribute
+    # absent keeps `hasattr` honest, where storing None would not
+    if mgf is not None:
+        self.pose_distance_figure = mgf
     return mgf