diff --git a/app/app.spec.js b/app/app.spec.js
index f41fb11..792b20f 100644
--- a/app/app.spec.js
+++ b/app/app.spec.js
@@ -106,4 +106,13 @@ describe('AppVue', () => {
       expect(game.step).toHaveBeenCalledTimes(1)
     })
   })
+
+  describe('moving the mouse with left button pressed in the viewport', () => {
+    beforeEach(async () => {
+      await wrapper.find('div').trigger('mousemove', { x: 0, y: 0, buttons: 1 })
+    })
+    test('should call game.mouseDown', () => {
+      expect(game.addCellAtPixel).toHaveBeenCalledTimes(1)
+    })
+  })
 })
diff --git a/app/app.vue b/app/app.vue
index 271b516..fe3033c 100644
--- a/app/app.vue
+++ b/app/app.vue
@@ -1,7 +1,10 @@
 <template>
   <Layout>
     <template #default>
-      <div ref="viewport" />
+      <div
+        ref="viewport"
+        @mousemove="handleMouseMove"
+      />
     </template>
     <template #ui>
       <div class="box">
@@ -80,6 +83,9 @@ export default {
     this.switchRunning()
   },
   methods: {
+    handleMouseMove (mouseEvent) {
+      if (mouseEvent.buttons === 1) game.addCellAtPixel(mouseEvent.offsetX, mouseEvent.offsetY)
+    },
     stepAnimate () {
       game.step()
     },
diff --git a/app/game/__mocks__/game.js b/app/game/__mocks__/game.js
index 6305c2f..97415c2 100644
--- a/app/game/__mocks__/game.js
+++ b/app/game/__mocks__/game.js
@@ -4,6 +4,7 @@ import Board from '../board.js'
 
 export default function Game () {
   const obj = {
+    addCellAtPixel: jest.fn(),
     step: jest.fn(),
     setViewportMock: jest.fn(),
     getBoardMock: jest.fn(),
diff --git a/app/game/__tests__/board.spec.js b/app/game/__tests__/board.spec.js
index 55dee34..249d2ff 100644
--- a/app/game/__tests__/board.spec.js
+++ b/app/game/__tests__/board.spec.js
@@ -42,4 +42,9 @@ describe('Board', () => {
       expect(new Board().pixelHeight).toEqual(800)
     })
   })
+  describe('pixelToCellCoordinates', () => {
+    test('should convert pixel coordinates to cell coordinates', () => {
+      expect(new Board().pixelToCellCoordinates(100, 100)).toEqual([50, 50])
+    })
+  })
 })
diff --git a/app/game/__tests__/game.spec.js b/app/game/__tests__/game.spec.js
index b6ba77f..8569aa8 100644
--- a/app/game/__tests__/game.spec.js
+++ b/app/game/__tests__/game.spec.js
@@ -148,4 +148,15 @@ describe('Game', () => {
       expect(game._animation.mainLoop).toHaveBeenCalledTimes(1)
     })
   })
+  describe('addCellAtPixel method', () => {
+    beforeEach(() => {
+      game._grid.resurectCell = jest.fn()
+      game._renderer = { render: jest.fn() }
+      game.addCellAtPixel({ x: 0, y: 0 })
+    })
+    test('should call grid.addCellAtPixel', () => {
+      expect(game._grid.resurectCell).toHaveBeenCalledTimes(1)
+      expect(game._renderer.render).toHaveBeenCalledTimes(1)
+    })
+  })
 })
diff --git a/app/game/__tests__/grid-utils.spec.js b/app/game/__tests__/grid-utils.spec.js
index 59bbd84..afcffdb 100644
--- a/app/game/__tests__/grid-utils.spec.js
+++ b/app/game/__tests__/grid-utils.spec.js
@@ -1,6 +1,6 @@
 import { describe, beforeEach, test, expect } from '@jest/globals'
 
-import { random, clear, indexToXy, xyToIndex } from '../grid-utils.js'
+import { random, clear, indexToXy, xyToIndex, resurect } from '../grid-utils.js'
 
 import {
   getState,
@@ -59,4 +59,13 @@ describe('Grid utils', () => {
       expect(indexToXy(gridLength, gridSide, 0 + gridSide * 3)).toEqual({ x: 0, y: 3 })
     })
   })
+  describe('resurectCell ()', () => {
+    test('should resurect cell', () => {
+      cells[0] = setState(cells[0], 0)
+      cells[1] = setState(cells[1], 0)
+      resurect(cells, 0)
+      expect(getState(cells[0])).toEqual(1)
+      expect(getState(cells[1])).toEqual(0)
+    })
+  })
 })
diff --git a/app/game/__tests__/grid.spec.js b/app/game/__tests__/grid.spec.js
index cb35368..b8e341e 100644
--- a/app/game/__tests__/grid.spec.js
+++ b/app/game/__tests__/grid.spec.js
@@ -1,5 +1,5 @@
 import { describe, beforeEach, afterEach, test, expect, jest } from '@jest/globals'
-import { random, clear, indexToXy, xyToIndex } from '../grid-utils.js'
+import { random, clear, indexToXy, xyToIndex, resurect } from '../grid-utils.js'
 
 import Grid from '../grid'
 import Rules from '../rules'
@@ -58,4 +58,13 @@ describe.each([
       expect(xyToIndex).toBeCalledWith(grid.length, grid.sizeX, 2, 2)
     })
   })
+  describe('resurectCell ()', () => {
+    test('should call resurect with instance parameters', () => {
+      const grid = new GridImplementation({ gridWidth: gridSide, gridHeight: gridSide }, new Rules())
+      xyToIndex.mockReturnValue(4)
+      grid.resurectCell(2, 2)
+      expect(xyToIndex).toBeCalledWith(grid.length, grid.sizeX, 2, 2)
+      expect(resurect).toBeCalledWith(grid.cells, 4)
+    })
+  })
 })
diff --git a/app/game/board.js b/app/game/board.js
index 6a3ed6c..fceb3ae 100644
--- a/app/game/board.js
+++ b/app/game/board.js
@@ -13,4 +13,18 @@ export default class Board {
   get pixelHeight () {
     return this.gridHeight * this.cellRadius
   }
+
+  /**
+   * Convert pixel coordinates to cell coordinates.
+   *
+   * @param {number} x - Mouse x coordinate in pixels, relative to the board.
+   * @param {number} y - Mouse y coordinate in pixels, relative to the board.
+   * @returns {[number, number]} - Cell coordinates.
+   */
+  pixelToCellCoordinates (x, y) {
+    return [
+      Math.floor(x / this.cellRadius),
+      Math.floor(y / this.cellRadius)
+    ]
+  }
 }
diff --git a/app/game/game.js b/app/game/game.js
index 3937e73..8defe9c 100644
--- a/app/game/game.js
+++ b/app/game/game.js
@@ -38,6 +38,22 @@ export default class Game {
     this._animation.mainLoop()
   }
 
+  /**
+   * Add a cell to the grid.
+   *
+   * @param {number} x - Mouse x coordinate in pixels, relative to the viewport element.
+   * @param {number} y - Mouse y coordinate in pixels, relative to the viewport element.
+   */
+  addCellAtPixel (x, y) {
+    this._grid.resurectCell(...this._board.pixelToCellCoordinates(x, y))
+    this._renderer.render()
+  }
+
+  /**
+   * Set the viewport.
+   *
+   * @param {Element} viewport - Viewport DOM element.
+   */
   // eslint-disable-next-line accessor-pairs
   set viewport (viewport) {
     this._viewport = viewport
diff --git a/app/game/grid-utils.js b/app/game/grid-utils.js
index 5c0537e..4a3f293 100644
--- a/app/game/grid-utils.js
+++ b/app/game/grid-utils.js
@@ -40,3 +40,7 @@ export function indexToXy (length, sizeX, i) {
 export function xyToIndex (length, sizeX, x, y) {
   return (sizeX * y + x) % length
 }
+
+export function resurect (cells, i) {
+  cells[i] = setState(cells[i], 1)
+}
diff --git a/app/game/grid.js b/app/game/grid.js
index bea265f..b045d82 100644
--- a/app/game/grid.js
+++ b/app/game/grid.js
@@ -5,7 +5,6 @@ const defaultName = typeof SharedArrayBuffer !== 'undefined' ? 'one-worker' : 'n
 const Grid = {
 
   load: async function (name = defaultName) {
-    console.log(`Load ${name} grid.`)
     implementation = await import(`./grids/grid-${name}`)
   },
 
diff --git a/app/game/grids/abstract-grid.js b/app/game/grids/abstract-grid.js
index 556f1ec..a41bc16 100644
--- a/app/game/grids/abstract-grid.js
+++ b/app/game/grids/abstract-grid.js
@@ -1,5 +1,5 @@
 import update from '../grid-updater.js'
-import { random, clear, indexToXy, xyToIndex } from '../grid-utils.js'
+import { random, clear, indexToXy, xyToIndex, resurect } from '../grid-utils.js'
 
 /**
  * Implements the game algorithm.
@@ -49,4 +49,8 @@ export default class {
   xyToIndex (x, y) {
     return xyToIndex(this.length, this.sizeX, x, y)
   }
+
+  resurectCell (x, y) {
+    resurect(this.cells, this.xyToIndex(x, y))
+  }
 }