diff --git a/web/markdown/markdown-spoiler.react.js b/web/markdown/markdown-spoiler.react.js
--- a/web/markdown/markdown-spoiler.react.js
+++ b/web/markdown/markdown-spoiler.react.js
@@ -13,7 +13,17 @@
 function MarkdownSpoiler(props: MarkdownSpoilerProps): React.Node {
   const { text } = props;
 
-  return <span className={css.spoiler}>{text}</span>;
+  const [spoilerClassName, setSpoilerClassName] = React.useState(css.spoiler);
+
+  const onSpoilerClick = React.useCallback(() => {
+    setSpoilerClassName(css.revealSpoilerAnimation);
+  }, [setSpoilerClassName]);
+
+  return (
+    <span className={spoilerClassName} onClick={onSpoilerClick}>
+      {text}
+    </span>
+  );
 }
 
 const MemoizedMarkdownSpoiler: React.ComponentType<MarkdownSpoilerProps> = React.memo<MarkdownSpoilerProps>(
diff --git a/web/markdown/markdown.css b/web/markdown/markdown.css
--- a/web/markdown/markdown.css
+++ b/web/markdown/markdown.css
@@ -44,6 +44,19 @@
   color: #33332c;
   cursor: pointer;
 }
+span.revealSpoilerAnimation {
+  animation: revealSpoiler 1s;
+}
+@keyframes revealSpoiler {
+  from {
+    background: #33332c;
+    color: #33332c;
+  }
+  to {
+    background: transparent;
+    color: white;
+  }
+}
 
 div.markdown pre {
   padding: 0.5em 10px;